syzbot has found a kernel BUG in ocfs2_write_cluster_by_desc,
while the next patch in the series resolves this, another
bug has been detected due to a potential deadlock [1].

The scenario is depicted here,

	CPU0					CPU1
lock(&ocfs2_file_ip_alloc_sem_key);
                               lock(&osb->system_file_mutex);
                               lock(&ocfs2_file_ip_alloc_sem_key);
lock(&osb->system_file_mutex);

The function calls which could lead to this are:

CPU0
ocfs2_write_begin - lock(&ocfs2_file_ip_alloc_sem_key);
.
.
.
ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);

CPU1 -
ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
.
.
.
ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);

This issue can be resolved by making the down_read -> down_read_try
in the ocfs2_read_virt_blocks.

[1] https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6

Reported-and-tested-by: syzbot+18a87160c7d64ba2e2f6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6
Signed-off-by: Mohammed Anees <pvmohammedanees2003@gmail.com>
---
 fs/ocfs2/extent_map.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index 70a768b62..f83d0a3b6 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/fiemap.h>
+#include <linux/delay.h>
 
 #include <cluster/masklog.h>
 
@@ -961,6 +962,8 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
 	int rc = 0;
 	u64 p_block, p_count;
 	int i, count, done = 0;
+	int retries, max_retries = 5;
+	int retry_delay_ms = 30;
 
 	trace_ocfs2_read_virt_blocks(
 	     inode, (unsigned long long)v_block, nr, bhs, flags,
@@ -973,7 +976,18 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
 	}
 
 	while (done < nr) {
-		down_read(&OCFS2_I(inode)->ip_alloc_sem);
+		retries = 0;
+		while (retries < max_retries) {
+			if (down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem))
+				break; // Lock acquired
+			msleep(retry_delay_ms);
+			retries++;
+		}
+		if (retries == max_retries) {
+			rc = -EAGAIN;
+			mlog(ML_ERROR, "Cannot acquire lock\n");
+			break;
+		}
 		rc = ocfs2_extent_map_get_blocks(inode, v_block + done,
 						 &p_block, &p_count, NULL);
 		up_read(&OCFS2_I(inode)->ip_alloc_sem);
-- 
2.46.0

On 9/19/24 01:20, Mohammed Anees wrote:
> syzbot has found a kernel BUG in ocfs2_write_cluster_by_desc,
> while the next patch in the series resolves this, another
> bug has been detected due to a potential deadlock [1].
> 
> The scenario is depicted here,
> 
> 	CPU0					CPU1
> lock(&ocfs2_file_ip_alloc_sem_key);
>                                 lock(&osb->system_file_mutex);
>                                 lock(&ocfs2_file_ip_alloc_sem_key);
> lock(&osb->system_file_mutex);
> 
> The function calls which could lead to this are:
> 
> CPU0
> ocfs2_write_begin - lock(&ocfs2_file_ip_alloc_sem_key);
> .
> .
> .
> ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
> 
> CPU1 -
> ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
> .
> .
> .
> ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);
> 
> This issue can be resolved by making the down_read -> down_read_try
> in the ocfs2_read_virt_blocks.
> 
> [1] https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6

I haven't checked this patch, but in my view, following URL is correct.
https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd

Heming
> 
> Reported-and-tested-by: syzbot+18a87160c7d64ba2e2f6@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6
> Signed-off-by: Mohammed Anees <pvmohammedanees2003@gmail.com>
> ---
>   fs/ocfs2/extent_map.c | 16 +++++++++++++++-
>   1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
> index 70a768b62..f83d0a3b6 100644
> --- a/fs/ocfs2/extent_map.c
> +++ b/fs/ocfs2/extent_map.c
> @@ -12,6 +12,7 @@
>   #include <linux/slab.h>
>   #include <linux/types.h>
>   #include <linux/fiemap.h>
> +#include <linux/delay.h>
>   
>   #include <cluster/masklog.h>
>   
> @@ -961,6 +962,8 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
>   	int rc = 0;
>   	u64 p_block, p_count;
>   	int i, count, done = 0;
> +	int retries, max_retries = 5;
> +	int retry_delay_ms = 30;
>   
>   	trace_ocfs2_read_virt_blocks(
>   	     inode, (unsigned long long)v_block, nr, bhs, flags,
> @@ -973,7 +976,18 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
>   	}
>   
>   	while (done < nr) {
> -		down_read(&OCFS2_I(inode)->ip_alloc_sem);
> +		retries = 0;
> +		while (retries < max_retries) {
> +			if (down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem))
> +				break; // Lock acquired
> +			msleep(retry_delay_ms);
> +			retries++;
> +		}
> +		if (retries == max_retries) {
> +			rc = -EAGAIN;
> +			mlog(ML_ERROR, "Cannot acquire lock\n");
> +			break;
> +		}
>   		rc = ocfs2_extent_map_get_blocks(inode, v_block + done,
>   						 &p_block, &p_count, NULL);
>   		up_read(&OCFS2_I(inode)->ip_alloc_sem);

Hi,
I tested the patch on the URL you have provided, it seems to
tackle the bug and it is appropriate, i will link this to that
URL and send the new patch.
Thanks!