[v2] erofs: reliably distinguish block based and fscache mode

[PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Baokun Li 2 weeks ago

When erofs_kill_sb() is called in block dev based mode, s_bdev may not have
been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it will
be mistaken for fscache mode, and then attempt to free an anon_dev that has
never been allocated, triggering the following warning:

============================================
ida_free called for id=0 which is not allocated.
WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
Modules linked in:
CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
RIP: 0010:ida_free+0x134/0x140
Call Trace:
 <TASK>
 erofs_kill_sb+0x81/0x90
 deactivate_locked_super+0x35/0x80
 get_tree_bdev+0x136/0x1e0
 vfs_get_tree+0x2c/0xf0
 do_new_mount+0x190/0x2f0
 [...]
============================================

Instead of allocating the erofs_sb_info in fill_super() allocate it
during erofs_get_tree() and ensure that erofs can always have the info
available during erofs_kill_sb().

Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
Changes since v1:
  Allocate and initialise fc->s_fs_info in erofs_fc_get_tree() instead of
  modifying fc->sb_flags.

V1: https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/

 fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 23 deletions(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index b21bd8f78dc1..4104280be2ea 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -581,8 +581,7 @@ static const struct export_operations erofs_export_ops = {
 static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct inode *inode;
-	struct erofs_sb_info *sbi;
-	struct erofs_fs_context *ctx = fc->fs_private;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
 	int err;
 
 	sb->s_magic = EROFS_SUPER_MAGIC;
@@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	sb->s_op = &erofs_sops;
 
-	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
-	if (!sbi)
-		return -ENOMEM;
-
-	sb->s_fs_info = sbi;
-	sbi->opt = ctx->opt;
-	sbi->devs = ctx->devs;
-	ctx->devs = NULL;
-	sbi->fsid = ctx->fsid;
-	ctx->fsid = NULL;
-	sbi->domain_id = ctx->domain_id;
-	ctx->domain_id = NULL;
-
 	sbi->blkszbits = PAGE_SHIFT;
 	if (erofs_is_fscache_mode(sb)) {
 		sb->s_blocksize = PAGE_SIZE;
@@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	return 0;
 }
 
-static int erofs_fc_get_tree(struct fs_context *fc)
+static void erofs_ctx_to_info(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx = fc->fs_private;
+	struct erofs_sb_info *sbi = fc->s_fs_info;
+
+	sbi->opt = ctx->opt;
+	sbi->devs = ctx->devs;
+	ctx->devs = NULL;
+	sbi->fsid = ctx->fsid;
+	ctx->fsid = NULL;
+	sbi->domain_id = ctx->domain_id;
+	ctx->domain_id = NULL;
+}
 
-	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->fsid)
+static int erofs_fc_get_tree(struct fs_context *fc)
+{
+	struct erofs_sb_info *sbi;
+
+	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
+	if (!sbi)
+		return -ENOMEM;
+
+	fc->s_fs_info = sbi;
+	erofs_ctx_to_info(fc);
+
+	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
 		return get_tree_nodev(fc, erofs_fc_fill_super);
 
 	return get_tree_bdev(fc, erofs_fc_fill_super);
@@ -767,6 +774,7 @@ static void erofs_fc_free(struct fs_context *fc)
 	kfree(ctx->fsid);
 	kfree(ctx->domain_id);
 	kfree(ctx);
+	kfree(fc->s_fs_info);
 }
 
 static const struct fs_context_operations erofs_context_ops = {
@@ -783,6 +791,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
+
 	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
 	if (!ctx->devs) {
 		kfree(ctx);
@@ -799,17 +808,13 @@ static int erofs_init_fs_context(struct fs_context *fc)
 
 static void erofs_kill_sb(struct super_block *sb)
 {
-	struct erofs_sb_info *sbi;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
 
-	if (erofs_is_fscache_mode(sb))
+	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
 		kill_anon_super(sb);
 	else
 		kill_block_super(sb);
 
-	sbi = EROFS_SB(sb);
-	if (!sbi)
-		return;
-
 	erofs_free_dev_context(sbi->devs);
 	fs_put_dax(sbi->dax_dev, NULL);
 	erofs_fscache_unregister_fs(sb);
-- 
2.31.1

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Jingbo Xu 2 weeks ago

Hi Baokun,

Thanks for catching this and move forward fixing this!


On 4/17/24 2:55 PM, Baokun Li wrote:
> When erofs_kill_sb() is called in block dev based mode, s_bdev may not have
> been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it will
> be mistaken for fscache mode, and then attempt to free an anon_dev that has
> never been allocated, triggering the following warning:
> 
> ============================================
> ida_free called for id=0 which is not allocated.
> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
> Modules linked in:
> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
> RIP: 0010:ida_free+0x134/0x140
> Call Trace:
>  <TASK>
>  erofs_kill_sb+0x81/0x90
>  deactivate_locked_super+0x35/0x80
>  get_tree_bdev+0x136/0x1e0
>  vfs_get_tree+0x2c/0xf0
>  do_new_mount+0x190/0x2f0
>  [...]
> ============================================
> 
> Instead of allocating the erofs_sb_info in fill_super() allocate it
> during erofs_get_tree() and ensure that erofs can always have the info
> available during erofs_kill_sb().


I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
another potential advantage of doing this way is that erofs_fs_context
is not needed anymore and we can use sbi directly.


> 
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
> Changes since v1:
>   Allocate and initialise fc->s_fs_info in erofs_fc_get_tree() instead of
>   modifying fc->sb_flags.
> 
> V1: https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
> 
>  fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
>  1 file changed, 28 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index b21bd8f78dc1..4104280be2ea 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -581,8 +581,7 @@ static const struct export_operations erofs_export_ops = {
>  static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  {
>  	struct inode *inode;
> -	struct erofs_sb_info *sbi;
> -	struct erofs_fs_context *ctx = fc->fs_private;
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  	int err;
>  
>  	sb->s_magic = EROFS_SUPER_MAGIC;
> @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sb->s_maxbytes = MAX_LFS_FILESIZE;
>  	sb->s_op = &erofs_sops;
>  
> -	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> -	if (!sbi)
> -		return -ENOMEM;
> -
> -	sb->s_fs_info = sbi;
> -	sbi->opt = ctx->opt;
> -	sbi->devs = ctx->devs;
> -	ctx->devs = NULL;
> -	sbi->fsid = ctx->fsid;
> -	ctx->fsid = NULL;
> -	sbi->domain_id = ctx->domain_id;
> -	ctx->domain_id = NULL;
> -
>  	sbi->blkszbits = PAGE_SHIFT;
>  	if (erofs_is_fscache_mode(sb)) {
>  		sb->s_blocksize = PAGE_SIZE;
> @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  	return 0;
>  }
>  
> -static int erofs_fc_get_tree(struct fs_context *fc)
> +static void erofs_ctx_to_info(struct fs_context *fc)
>  {
>  	struct erofs_fs_context *ctx = fc->fs_private;
> +	struct erofs_sb_info *sbi = fc->s_fs_info;
> +
> +	sbi->opt = ctx->opt;
> +	sbi->devs = ctx->devs;
> +	ctx->devs = NULL;
> +	sbi->fsid = ctx->fsid;
> +	ctx->fsid = NULL;
> +	sbi->domain_id = ctx->domain_id;
> +	ctx->domain_id = NULL;
> +}

I'm not sure if abstracting this logic into a seperate helper really
helps understanding the code as the logic itself is quite simple and
easy to be understood. Usually it's a hint of over-abstraction when a
simple helper has only one caller.


>  
> -	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->fsid)
> +static int erofs_fc_get_tree(struct fs_context *fc)
> +{
> +	struct erofs_sb_info *sbi;
> +
> +	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> +	if (!sbi)
> +		return -ENOMEM;
> +
> +	fc->s_fs_info = sbi;
> +	erofs_ctx_to_info(fc);
> +
> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>  		return get_tree_nodev(fc, erofs_fc_fill_super);
>  
>  	return get_tree_bdev(fc, erofs_fc_fill_super);
> @@ -767,6 +774,7 @@ static void erofs_fc_free(struct fs_context *fc)
>  	kfree(ctx->fsid);
>  	kfree(ctx->domain_id);
>  	kfree(ctx);
> +	kfree(fc->s_fs_info);
>  }
>  
>  static const struct fs_context_operations erofs_context_ops = {
> @@ -783,6 +791,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
>  	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>  	if (!ctx)
>  		return -ENOMEM;
> +
>  	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
>  	if (!ctx->devs) {
>  		kfree(ctx);
> @@ -799,17 +808,13 @@ static int erofs_init_fs_context(struct fs_context *fc)
>  
>  static void erofs_kill_sb(struct super_block *sb)
>  {
> -	struct erofs_sb_info *sbi;
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  
> -	if (erofs_is_fscache_mode(sb))
> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>  		kill_anon_super(sb);
>  	else
>  		kill_block_super(sb);
>  
> -	sbi = EROFS_SB(sb);
> -	if (!sbi)
> -		return;
> -
>  	erofs_free_dev_context(sbi->devs);
>  	fs_put_dax(sbi->dax_dev, NULL);
>  	erofs_fscache_unregister_fs(sb);

-- 
Thanks,
Jingbo

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Baokun Li 2 weeks ago

On 2024/4/18 10:16, Jingbo Xu wrote:
> Hi Baokun,
>
> Thanks for catching this and move forward fixing this!

Hi Jingbo，

Thanks for your review！

>
> On 4/17/24 2:55 PM, Baokun Li wrote:
>> When erofs_kill_sb() is called in block dev based mode, s_bdev may not have
>> been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it will
>> be mistaken for fscache mode, and then attempt to free an anon_dev that has
>> never been allocated, triggering the following warning:
>>
>> ============================================
>> ida_free called for id=0 which is not allocated.
>> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
>> Modules linked in:
>> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
>> RIP: 0010:ida_free+0x134/0x140
>> Call Trace:
>>   <TASK>
>>   erofs_kill_sb+0x81/0x90
>>   deactivate_locked_super+0x35/0x80
>>   get_tree_bdev+0x136/0x1e0
>>   vfs_get_tree+0x2c/0xf0
>>   do_new_mount+0x190/0x2f0
>>   [...]
>> ============================================
>>
>> Instead of allocating the erofs_sb_info in fill_super() allocate it
>> during erofs_get_tree() and ensure that erofs can always have the info
>> available during erofs_kill_sb().
>
> I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
> be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
> another potential advantage of doing this way is that erofs_fs_context
> is not needed anymore and we can use sbi directly.
Yes, except for some extra memory usage when remounting,
this idea sounds great. Let me send a version of v3 to get rid
of erofs_fs_context.
>
>> Signed-off-by: Christian Brauner <brauner@kernel.org>
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>> ---
>> Changes since v1:
>>    Allocate and initialise fc->s_fs_info in erofs_fc_get_tree() instead of
>>    modifying fc->sb_flags.
>>
>> V1: https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
>>
>>   fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
>>   1 file changed, 28 insertions(+), 23 deletions(-)
>>
>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>> index b21bd8f78dc1..4104280be2ea 100644
>> --- a/fs/erofs/super.c
>> +++ b/fs/erofs/super.c
>> @@ -581,8 +581,7 @@ static const struct export_operations erofs_export_ops = {
>>   static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>>   {
>>   	struct inode *inode;
>> -	struct erofs_sb_info *sbi;
>> -	struct erofs_fs_context *ctx = fc->fs_private;
>> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>>   	int err;
>>   
>>   	sb->s_magic = EROFS_SUPER_MAGIC;
>> @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>>   	sb->s_maxbytes = MAX_LFS_FILESIZE;
>>   	sb->s_op = &erofs_sops;
>>   
>> -	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>> -	if (!sbi)
>> -		return -ENOMEM;
>> -
>> -	sb->s_fs_info = sbi;
>> -	sbi->opt = ctx->opt;
>> -	sbi->devs = ctx->devs;
>> -	ctx->devs = NULL;
>> -	sbi->fsid = ctx->fsid;
>> -	ctx->fsid = NULL;
>> -	sbi->domain_id = ctx->domain_id;
>> -	ctx->domain_id = NULL;
>> -
>>   	sbi->blkszbits = PAGE_SHIFT;
>>   	if (erofs_is_fscache_mode(sb)) {
>>   		sb->s_blocksize = PAGE_SIZE;
>> @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>>   	return 0;
>>   }
>>   
>> -static int erofs_fc_get_tree(struct fs_context *fc)
>> +static void erofs_ctx_to_info(struct fs_context *fc)
>>   {
>>   	struct erofs_fs_context *ctx = fc->fs_private;
>> +	struct erofs_sb_info *sbi = fc->s_fs_info;
>> +
>> +	sbi->opt = ctx->opt;
>> +	sbi->devs = ctx->devs;
>> +	ctx->devs = NULL;
>> +	sbi->fsid = ctx->fsid;
>> +	ctx->fsid = NULL;
>> +	sbi->domain_id = ctx->domain_id;
>> +	ctx->domain_id = NULL;
>> +}
> I'm not sure if abstracting this logic into a seperate helper really
> helps understanding the code as the logic itself is quite simple and
> easy to be understood. Usually it's a hint of over-abstraction when a
> simple helper has only one caller.
>
Static functions that have only one caller are compiled inline, so we
don't have to worry about how that affects the code.

The reason these codes are encapsulated in a separate function is so
that the code reader understands that these codes are integrated
as a whole, and that we shouldn't have to move one or two of these
lines individually.

But after we get rid of erofs_fs_context, those won't be needed
anymore.
>>   
>> -	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->fsid)
>> +static int erofs_fc_get_tree(struct fs_context *fc)
>> +{
>> +	struct erofs_sb_info *sbi;
>> +
>> +	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>> +	if (!sbi)
>> +		return -ENOMEM;
>> +
>> +	fc->s_fs_info = sbi;
>> +	erofs_ctx_to_info(fc);
>> +
>> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>>   		return get_tree_nodev(fc, erofs_fc_fill_super);
>>   
>>   	return get_tree_bdev(fc, erofs_fc_fill_super);
>> @@ -767,6 +774,7 @@ static void erofs_fc_free(struct fs_context *fc)
>>   	kfree(ctx->fsid);
>>   	kfree(ctx->domain_id);
>>   	kfree(ctx);
>> +	kfree(fc->s_fs_info);
>>   }
>>   
>>   static const struct fs_context_operations erofs_context_ops = {
>> @@ -783,6 +791,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
>>   	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>>   	if (!ctx)
>>   		return -ENOMEM;
>> +
>>   	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
>>   	if (!ctx->devs) {
>>   		kfree(ctx);
>> @@ -799,17 +808,13 @@ static int erofs_init_fs_context(struct fs_context *fc)
>>   
>>   static void erofs_kill_sb(struct super_block *sb)
>>   {
>> -	struct erofs_sb_info *sbi;
>> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>>   
>> -	if (erofs_is_fscache_mode(sb))
>> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>>   		kill_anon_super(sb);
>>   	else
>>   		kill_block_super(sb);
>>   
>> -	sbi = EROFS_SB(sb);
>> -	if (!sbi)
>> -		return;
>> -
>>   	erofs_free_dev_context(sbi->devs);
>>   	fs_put_dax(sbi->dax_dev, NULL);
>>   	erofs_fscache_unregister_fs(sb);
-- 
With Best Regards,
Baokun Li

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Jingbo Xu 1 week, 6 days ago


On 4/18/24 11:36 AM, Baokun Li wrote:
> On 2024/4/18 10:16, Jingbo Xu wrote:
>> Hi Baokun,
>>
>> Thanks for catching this and move forward fixing this!
> 
> Hi Jingbo，
> 
> Thanks for your review！
> 
>>
>> On 4/17/24 2:55 PM, Baokun Li wrote:
>>> When erofs_kill_sb() is called in block dev based mode, s_bdev may
>>> not have
>>> been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it
>>> will
>>> be mistaken for fscache mode, and then attempt to free an anon_dev
>>> that has
>>> never been allocated, triggering the following warning:
>>>
>>> ============================================
>>> ida_free called for id=0 which is not allocated.
>>> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
>>> Modules linked in:
>>> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
>>> RIP: 0010:ida_free+0x134/0x140
>>> Call Trace:
>>>   <TASK>
>>>   erofs_kill_sb+0x81/0x90
>>>   deactivate_locked_super+0x35/0x80
>>>   get_tree_bdev+0x136/0x1e0
>>>   vfs_get_tree+0x2c/0xf0
>>>   do_new_mount+0x190/0x2f0
>>>   [...]
>>> ============================================
>>>
>>> Instead of allocating the erofs_sb_info in fill_super() allocate it
>>> during erofs_get_tree() and ensure that erofs can always have the info
>>> available during erofs_kill_sb().
>>
>> I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
>> be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
>> another potential advantage of doing this way is that erofs_fs_context
>> is not needed anymore and we can use sbi directly.
> Yes, except for some extra memory usage when remounting,
> this idea sounds great. Let me send a version of v3 to get rid
> of erofs_fs_context.

I'm not sure if Gao Xaing also prefers this.  I think it would be better
to wait and listen for his thoughts before we sending v3.

>>
>>> Signed-off-by: Christian Brauner <brauner@kernel.org>
>>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>>> ---
>>> Changes since v1:
>>>    Allocate and initialise fc->s_fs_info in erofs_fc_get_tree()
>>> instead of
>>>    modifying fc->sb_flags.
>>>
>>> V1:
>>> https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
>>>
>>>   fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
>>>   1 file changed, 28 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>>> index b21bd8f78dc1..4104280be2ea 100644
>>> --- a/fs/erofs/super.c
>>> +++ b/fs/erofs/super.c
>>> @@ -581,8 +581,7 @@ static const struct export_operations
>>> erofs_export_ops = {
>>>   static int erofs_fc_fill_super(struct super_block *sb, struct
>>> fs_context *fc)
>>>   {
>>>       struct inode *inode;
>>> -    struct erofs_sb_info *sbi;
>>> -    struct erofs_fs_context *ctx = fc->fs_private;
>>> +    struct erofs_sb_info *sbi = EROFS_SB(sb);
>>>       int err;
>>>         sb->s_magic = EROFS_SUPER_MAGIC;
>>> @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct
>>> super_block *sb, struct fs_context *fc)
>>>       sb->s_maxbytes = MAX_LFS_FILESIZE;
>>>       sb->s_op = &erofs_sops;
>>>   -    sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>>> -    if (!sbi)
>>> -        return -ENOMEM;
>>> -
>>> -    sb->s_fs_info = sbi;
>>> -    sbi->opt = ctx->opt;
>>> -    sbi->devs = ctx->devs;
>>> -    ctx->devs = NULL;
>>> -    sbi->fsid = ctx->fsid;
>>> -    ctx->fsid = NULL;
>>> -    sbi->domain_id = ctx->domain_id;
>>> -    ctx->domain_id = NULL;
>>> -
>>>       sbi->blkszbits = PAGE_SHIFT;
>>>       if (erofs_is_fscache_mode(sb)) {
>>>           sb->s_blocksize = PAGE_SIZE;
>>> @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct
>>> super_block *sb, struct fs_context *fc)
>>>       return 0;
>>>   }
>>>   -static int erofs_fc_get_tree(struct fs_context *fc)
>>> +static void erofs_ctx_to_info(struct fs_context *fc)
>>>   {
>>>       struct erofs_fs_context *ctx = fc->fs_private;
>>> +    struct erofs_sb_info *sbi = fc->s_fs_info;
>>> +
>>> +    sbi->opt = ctx->opt;
>>> +    sbi->devs = ctx->devs;
>>> +    ctx->devs = NULL;
>>> +    sbi->fsid = ctx->fsid;
>>> +    ctx->fsid = NULL;
>>> +    sbi->domain_id = ctx->domain_id;
>>> +    ctx->domain_id = NULL;
>>> +}
>> I'm not sure if abstracting this logic into a seperate helper really
>> helps understanding the code as the logic itself is quite simple and
>> easy to be understood. Usually it's a hint of over-abstraction when a
>> simple helper has only one caller.
>>
> Static functions that have only one caller are compiled inline, so we
> don't have to worry about how that affects the code.
> 
> The reason these codes are encapsulated in a separate function is so
> that the code reader understands that these codes are integrated
> as a whole, and that we shouldn't have to move one or two of these
> lines individually.
> 
> But after we get rid of erofs_fs_context, those won't be needed
> anymore.

Yeah, I understand. It's only coding style concerns.



-- 
Thanks,
Jingbo

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Baokun Li 1 week, 6 days ago

On 2024/4/18 13:50, Jingbo Xu wrote:
>
> On 4/18/24 11:36 AM, Baokun Li wrote:
>> On 2024/4/18 10:16, Jingbo Xu wrote:
>>> Hi Baokun,
>>>
>>> Thanks for catching this and move forward fixing this!
>> Hi Jingbo，
>>
>> Thanks for your review！
>>
>>> On 4/17/24 2:55 PM, Baokun Li wrote:
>>>> When erofs_kill_sb() is called in block dev based mode, s_bdev may
>>>> not have
>>>> been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it
>>>> will
>>>> be mistaken for fscache mode, and then attempt to free an anon_dev
>>>> that has
>>>> never been allocated, triggering the following warning:
>>>>
>>>> ============================================
>>>> ida_free called for id=0 which is not allocated.
>>>> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
>>>> Modules linked in:
>>>> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
>>>> RIP: 0010:ida_free+0x134/0x140
>>>> Call Trace:
>>>>    <TASK>
>>>>    erofs_kill_sb+0x81/0x90
>>>>    deactivate_locked_super+0x35/0x80
>>>>    get_tree_bdev+0x136/0x1e0
>>>>    vfs_get_tree+0x2c/0xf0
>>>>    do_new_mount+0x190/0x2f0
>>>>    [...]
>>>> ============================================
>>>>
>>>> Instead of allocating the erofs_sb_info in fill_super() allocate it
>>>> during erofs_get_tree() and ensure that erofs can always have the info
>>>> available during erofs_kill_sb().
>>> I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
>>> be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
>>> another potential advantage of doing this way is that erofs_fs_context
>>> is not needed anymore and we can use sbi directly.
>> Yes, except for some extra memory usage when remounting,
>> this idea sounds great. Let me send a version of v3 to get rid
>> of erofs_fs_context.
> I'm not sure if Gao Xaing also prefers this.  I think it would be better
> to wait and listen for his thoughts before we sending v3.
  Okay, there's no rush on this.
>>>> Signed-off-by: Christian Brauner <brauner@kernel.org>
>>>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>>>> ---
>>>> Changes since v1:
>>>>     Allocate and initialise fc->s_fs_info in erofs_fc_get_tree()
>>>> instead of
>>>>     modifying fc->sb_flags.
>>>>
>>>> V1:
>>>> https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
>>>>
>>>>    fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
>>>>    1 file changed, 28 insertions(+), 23 deletions(-)
>>>>
>>>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>>>> index b21bd8f78dc1..4104280be2ea 100644
>>>> --- a/fs/erofs/super.c
>>>> +++ b/fs/erofs/super.c
>>>> @@ -581,8 +581,7 @@ static const struct export_operations
>>>> erofs_export_ops = {
>>>>    static int erofs_fc_fill_super(struct super_block *sb, struct
>>>> fs_context *fc)
>>>>    {
>>>>        struct inode *inode;
>>>> -    struct erofs_sb_info *sbi;
>>>> -    struct erofs_fs_context *ctx = fc->fs_private;
>>>> +    struct erofs_sb_info *sbi = EROFS_SB(sb);
>>>>        int err;
>>>>          sb->s_magic = EROFS_SUPER_MAGIC;
>>>> @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct
>>>> super_block *sb, struct fs_context *fc)
>>>>        sb->s_maxbytes = MAX_LFS_FILESIZE;
>>>>        sb->s_op = &erofs_sops;
>>>>    -    sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>>>> -    if (!sbi)
>>>> -        return -ENOMEM;
>>>> -
>>>> -    sb->s_fs_info = sbi;
>>>> -    sbi->opt = ctx->opt;
>>>> -    sbi->devs = ctx->devs;
>>>> -    ctx->devs = NULL;
>>>> -    sbi->fsid = ctx->fsid;
>>>> -    ctx->fsid = NULL;
>>>> -    sbi->domain_id = ctx->domain_id;
>>>> -    ctx->domain_id = NULL;
>>>> -
>>>>        sbi->blkszbits = PAGE_SHIFT;
>>>>        if (erofs_is_fscache_mode(sb)) {
>>>>            sb->s_blocksize = PAGE_SIZE;
>>>> @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct
>>>> super_block *sb, struct fs_context *fc)
>>>>        return 0;
>>>>    }
>>>>    -static int erofs_fc_get_tree(struct fs_context *fc)
>>>> +static void erofs_ctx_to_info(struct fs_context *fc)
>>>>    {
>>>>        struct erofs_fs_context *ctx = fc->fs_private;
>>>> +    struct erofs_sb_info *sbi = fc->s_fs_info;
>>>> +
>>>> +    sbi->opt = ctx->opt;
>>>> +    sbi->devs = ctx->devs;
>>>> +    ctx->devs = NULL;
>>>> +    sbi->fsid = ctx->fsid;
>>>> +    ctx->fsid = NULL;
>>>> +    sbi->domain_id = ctx->domain_id;
>>>> +    ctx->domain_id = NULL;
>>>> +}
>>> I'm not sure if abstracting this logic into a seperate helper really
>>> helps understanding the code as the logic itself is quite simple and
>>> easy to be understood. Usually it's a hint of over-abstraction when a
>>> simple helper has only one caller.
>>>
>> Static functions that have only one caller are compiled inline, so we
>> don't have to worry about how that affects the code.
>>
>> The reason these codes are encapsulated in a separate function is so
>> that the code reader understands that these codes are integrated
>> as a whole, and that we shouldn't have to move one or two of these
>> lines individually.
>>
>> But after we get rid of erofs_fs_context, those won't be needed
>> anymore.
> Yeah, I understand. It's only coding style concerns.
>
>
>
Okay, thanks！

-- 
With Best Regards,
Baokun Li

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Gao Xiang 1 week, 6 days ago

Hi,

On Thu, Apr 18, 2024 at 02:12:39PM +0800, Baokun Li wrote:
> On 2024/4/18 13:50, Jingbo Xu wrote:
> > 
> > On 4/18/24 11:36 AM, Baokun Li wrote:
> > > On 2024/4/18 10:16, Jingbo Xu wrote:
> > > > Hi Baokun,
> > > > 
> > > > Thanks for catching this and move forward fixing this!
> > > Hi Jingbo，
> > > 
> > > Thanks for your review！
> > > 
> > > > On 4/17/24 2:55 PM, Baokun Li wrote:
> > > > > When erofs_kill_sb() is called in block dev based mode, s_bdev may
> > > > > not have
> > > > > been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it
> > > > > will
> > > > > be mistaken for fscache mode, and then attempt to free an anon_dev
> > > > > that has
> > > > > never been allocated, triggering the following warning:
> > > > > 
> > > > > ============================================
> > > > > ida_free called for id=0 which is not allocated.
> > > > > WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
> > > > > Modules linked in:
> > > > > CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
> > > > > RIP: 0010:ida_free+0x134/0x140
> > > > > Call Trace:
> > > > >    <TASK>
> > > > >    erofs_kill_sb+0x81/0x90
> > > > >    deactivate_locked_super+0x35/0x80
> > > > >    get_tree_bdev+0x136/0x1e0
> > > > >    vfs_get_tree+0x2c/0xf0
> > > > >    do_new_mount+0x190/0x2f0
> > > > >    [...]
> > > > > ============================================
> > > > > 
> > > > > Instead of allocating the erofs_sb_info in fill_super() allocate it
> > > > > during erofs_get_tree() and ensure that erofs can always have the info
> > > > > available during erofs_kill_sb().
> > > > I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
> > > > be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
> > > > another potential advantage of doing this way is that erofs_fs_context
> > > > is not needed anymore and we can use sbi directly.
> > > Yes, except for some extra memory usage when remounting,
> > > this idea sounds great. Let me send a version of v3 to get rid
> > > of erofs_fs_context.
> > I'm not sure if Gao Xaing also prefers this.  I think it would be better
> > to wait and listen for his thoughts before we sending v3.
>  Okay, there's no rush on this.

I checked days ago, for example, XFS is also worked in this way.
And .reconfigure() needs to be carefully handled too.

> > > > > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > > > > Signed-off-by: Baokun Li <libaokun1@huawei.com>
> > > > > ---
> > > > > Changes since v1:
> > > > >     Allocate and initialise fc->s_fs_info in erofs_fc_get_tree()
> > > > > instead of
> > > > >     modifying fc->sb_flags.
> > > > > 
> > > > > V1:
> > > > > https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
> > > > > 
> > > > >    fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
> > > > >    1 file changed, 28 insertions(+), 23 deletions(-)
> > > > > 
> > > > > diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> > > > > index b21bd8f78dc1..4104280be2ea 100644
> > > > > --- a/fs/erofs/super.c
> > > > > +++ b/fs/erofs/super.c
> > > > > @@ -581,8 +581,7 @@ static const struct export_operations
> > > > > erofs_export_ops = {
> > > > >    static int erofs_fc_fill_super(struct super_block *sb, struct
> > > > > fs_context *fc)
> > > > >    {
> > > > >        struct inode *inode;
> > > > > -    struct erofs_sb_info *sbi;
> > > > > -    struct erofs_fs_context *ctx = fc->fs_private;
> > > > > +    struct erofs_sb_info *sbi = EROFS_SB(sb);
> > > > >        int err;
> > > > >          sb->s_magic = EROFS_SUPER_MAGIC;
> > > > > @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct
> > > > > super_block *sb, struct fs_context *fc)
> > > > >        sb->s_maxbytes = MAX_LFS_FILESIZE;
> > > > >        sb->s_op = &erofs_sops;
> > > > >    -    sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> > > > > -    if (!sbi)
> > > > > -        return -ENOMEM;
> > > > > -
> > > > > -    sb->s_fs_info = sbi;
> > > > > -    sbi->opt = ctx->opt;
> > > > > -    sbi->devs = ctx->devs;
> > > > > -    ctx->devs = NULL;
> > > > > -    sbi->fsid = ctx->fsid;
> > > > > -    ctx->fsid = NULL;
> > > > > -    sbi->domain_id = ctx->domain_id;
> > > > > -    ctx->domain_id = NULL;
> > > > > -
> > > > >        sbi->blkszbits = PAGE_SHIFT;
> > > > >        if (erofs_is_fscache_mode(sb)) {
> > > > >            sb->s_blocksize = PAGE_SIZE;
> > > > > @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct
> > > > > super_block *sb, struct fs_context *fc)
> > > > >        return 0;
> > > > >    }
> > > > >    -static int erofs_fc_get_tree(struct fs_context *fc)
> > > > > +static void erofs_ctx_to_info(struct fs_context *fc)
> > > > >    {
> > > > >        struct erofs_fs_context *ctx = fc->fs_private;
> > > > > +    struct erofs_sb_info *sbi = fc->s_fs_info;
> > > > > +
> > > > > +    sbi->opt = ctx->opt;
> > > > > +    sbi->devs = ctx->devs;
> > > > > +    ctx->devs = NULL;
> > > > > +    sbi->fsid = ctx->fsid;
> > > > > +    ctx->fsid = NULL;
> > > > > +    sbi->domain_id = ctx->domain_id;
> > > > > +    ctx->domain_id = NULL;
> > > > > +}
> > > > I'm not sure if abstracting this logic into a seperate helper really
> > > > helps understanding the code as the logic itself is quite simple and
> > > > easy to be understood. Usually it's a hint of over-abstraction when a
> > > > simple helper has only one caller.
> > > > 
> > > Static functions that have only one caller are compiled inline, so we
> > > don't have to worry about how that affects the code.
> > > 
> > > The reason these codes are encapsulated in a separate function is so
> > > that the code reader understands that these codes are integrated
> > > as a whole, and that we shouldn't have to move one or two of these
> > > lines individually.
> > > 
> > > But after we get rid of erofs_fs_context, those won't be needed
> > > anymore.
> > Yeah, I understand. It's only coding style concerns.
> > 
> > 
> > 
> Okay, thanks！

I'm fine to get rid of those (erofs_fs_context) as long as the codebase
is more clearer and simple.  BTW, for the current codebase, I also think
it's unneeded to have a separate helper called once without extra actual
meaning...

Thanks,
Gao Xiang

> 
> -- 
> With Best Regards,
> Baokun Li

Re: [PATCH v2] erofs: reliably distinguish block based and fscache mode

Posted by Baokun Li 1 week, 6 days ago

On 2024/4/18 15:49, Gao Xiang wrote:
> Hi,
>
> On Thu, Apr 18, 2024 at 02:12:39PM +0800, Baokun Li wrote:
>> On 2024/4/18 13:50, Jingbo Xu wrote:
>>> On 4/18/24 11:36 AM, Baokun Li wrote:
>>>> On 2024/4/18 10:16, Jingbo Xu wrote:
>>>>> Hi Baokun,
>>>>>
>>>>> Thanks for catching this and move forward fixing this!
>>>> Hi Jingbo，
>>>>
>>>> Thanks for your review！
>>>>
>>>>> On 4/17/24 2:55 PM, Baokun Li wrote:

SNIP

>>>>>
>>>>> Instead of allocating the erofs_sb_info in fill_super() allocate it
>>>>> during erofs_get_tree() and ensure that erofs can always have the info
>>>>> available during erofs_kill_sb().
>>>>> I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
>>>>> be better, as I see some filesystems (e.g. autofs) do this way.  Maybe
>>>>> another potential advantage of doing this way is that erofs_fs_context
>>>>> is not needed anymore and we can use sbi directly.
>>>> Yes, except for some extra memory usage when remounting,
>>>> this idea sounds great. Let me send a version of v3 to get rid
>>>> of erofs_fs_context.
>>> I'm not sure if Gao Xaing also prefers this.  I think it would be better
>>> to wait and listen for his thoughts before we sending v3.
>>   Okay, there's no rush on this.
> I checked days ago, for example, XFS is also worked in this way.
> And .reconfigure() needs to be carefully handled too.

Ok, I'll implement it in the next iteration.

>>>>>> +static void erofs_ctx_to_info(struct fs_context *fc)
>>>>>>     {
>>>>>>         struct erofs_fs_context *ctx = fc->fs_private;
>>>>>> +    struct erofs_sb_info *sbi = fc->s_fs_info;
>>>>>> +
>>>>>> +    sbi->opt = ctx->opt;
>>>>>> +    sbi->devs = ctx->devs;
>>>>>> +    ctx->devs = NULL;
>>>>>> +    sbi->fsid = ctx->fsid;
>>>>>> +    ctx->fsid = NULL;
>>>>>> +    sbi->domain_id = ctx->domain_id;
>>>>>> +    ctx->domain_id = NULL;
>>>>>> +}
>>>>> I'm not sure if abstracting this logic into a seperate helper really
>>>>> helps understanding the code as the logic itself is quite simple and
>>>>> easy to be understood. Usually it's a hint of over-abstraction when a
>>>>> simple helper has only one caller.
>>>>>
>>>> Static functions that have only one caller are compiled inline, so we
>>>> don't have to worry about how that affects the code.
>>>>
>>>> The reason these codes are encapsulated in a separate function is so
>>>> that the code reader understands that these codes are integrated
>>>> as a whole, and that we shouldn't have to move one or two of these
>>>> lines individually.
>>>>
>>>> But after we get rid of erofs_fs_context, those won't be needed
>>>> anymore.
>>> Yeah, I understand. It's only coding style concerns.
>>>
>>>
>>>
>> Okay, thanks！
> I'm fine to get rid of those (erofs_fs_context) as long as the codebase
> is more clearer and simple.  BTW, for the current codebase, I also think
> it's unneeded to have a separate helper called once without extra actual
> meaning...
>
> Thanks,
> Gao Xiang
>
Ok, this helper function will be gone in the next iteration.

Thanks for the review!
-- 
With Best Regards,
Baokun Li