[v1] lockdep: Correct lock_classes index mapping

[PATCH] lockdep: Correct lock_classes index mapping

Posted by Cheng Jui Wang 2 years, 7 months ago

A kernel exception was hit when trying to dump /proc/lockdep_chains after
lockdep report "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!":

Unable to handle kernel paging request at virtual address 00054005450e05c3
...
00054005450e05c3] address between user and kernel address ranges
...
pc : [0xffffffece769b3a8] string+0x50/0x10c
lr : [0xffffffece769ac88] vsnprintf+0x468/0x69c
...
 Call trace:
  string+0x50/0x10c
  vsnprintf+0x468/0x69c
  seq_printf+0x8c/0xd8
  print_name+0x64/0xf4
  lc_show+0xb8/0x128
  seq_read_iter+0x3cc/0x5fc
  proc_reg_read_iter+0xdc/0x1d4

The cause of the problem is the function lock_chain_get_class() will
shift lock_classes index by 1, but the index don't need to be shifted
anymore since commit 01bb6f0af992 ("locking/lockdep: Change the range of
class_idx in held_lock struct") already change the index to start from
0.

The lock_classes[-1] located at chain_hlocks array. When printing
lock_classes[-1] after the chain_hlocks entries are modified, the
exception happened.

The output of lockdep_chains are incorrect due to this problem too.

Fixes: f611e8cf98ec ("lockdep: Take read/write status in consideration when generate chainkey")

Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
---
 kernel/locking/lockdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4a882f83aeb9..f8a0212189ca 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3462,7 +3462,7 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 	u16 chain_hlock = chain_hlocks[chain->base + i];
 	unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
 
-	return lock_classes + class_idx - 1;
+	return lock_classes + class_idx;
 }
 
 /*
@@ -3530,7 +3530,7 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 		hlock_id = chain_hlocks[chain->base + i];
 		chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
-		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
+		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
 		printk("\n");
 	}
 }
-- 
2.18.0

Re: [PATCH] lockdep: Correct lock_classes index mapping

Posted by Greg KH 2 years, 7 months ago

On Thu, Feb 10, 2022 at 06:50:11PM +0800, Cheng Jui Wang wrote:
> A kernel exception was hit when trying to dump /proc/lockdep_chains after
> lockdep report "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!":
> 
> Unable to handle kernel paging request at virtual address 00054005450e05c3
> ...
> 00054005450e05c3] address between user and kernel address ranges
> ...
> pc : [0xffffffece769b3a8] string+0x50/0x10c
> lr : [0xffffffece769ac88] vsnprintf+0x468/0x69c
> ...
>  Call trace:
>   string+0x50/0x10c
>   vsnprintf+0x468/0x69c
>   seq_printf+0x8c/0xd8
>   print_name+0x64/0xf4
>   lc_show+0xb8/0x128
>   seq_read_iter+0x3cc/0x5fc
>   proc_reg_read_iter+0xdc/0x1d4
> 
> The cause of the problem is the function lock_chain_get_class() will
> shift lock_classes index by 1, but the index don't need to be shifted
> anymore since commit 01bb6f0af992 ("locking/lockdep: Change the range of
> class_idx in held_lock struct") already change the index to start from
> 0.
> 
> The lock_classes[-1] located at chain_hlocks array. When printing
> lock_classes[-1] after the chain_hlocks entries are modified, the
> exception happened.
> 
> The output of lockdep_chains are incorrect due to this problem too.
> 
> Fixes: f611e8cf98ec ("lockdep: Take read/write status in consideration when generate chainkey")
> 
> Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
> ---
>  kernel/locking/lockdep.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 4a882f83aeb9..f8a0212189ca 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3462,7 +3462,7 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
>  	u16 chain_hlock = chain_hlocks[chain->base + i];
>  	unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
>  
> -	return lock_classes + class_idx - 1;
> +	return lock_classes + class_idx;
>  }
>  
>  /*
> @@ -3530,7 +3530,7 @@ static void print_chain_keys_chain(struct lock_chain *chain)
>  		hlock_id = chain_hlocks[chain->base + i];
>  		chain_key = print_chain_key_iteration(hlock_id, chain_key);
>  
> -		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
> +		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
>  		printk("\n");
>  	}
>  }
> -- 
> 2.18.0
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

[tip: locking/urgent] lockdep: Correct lock_classes index mapping

Posted by tip-bot2 for Cheng Jui Wang 2 years, 7 months ago

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     28df029d53a2fd80c1b8674d47895648ad26dcfb
Gitweb:        https://git.kernel.org/tip/28df029d53a2fd80c1b8674d47895648ad26dcfb
Author:        Cheng Jui Wang <cheng-jui.wang@mediatek.com>
AuthorDate:    Thu, 10 Feb 2022 18:50:11 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 11 Feb 2022 23:30:02 +01:00

lockdep: Correct lock_classes index mapping

A kernel exception was hit when trying to dump /proc/lockdep_chains after
lockdep report "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!":

Unable to handle kernel paging request at virtual address 00054005450e05c3
...
00054005450e05c3] address between user and kernel address ranges
...
pc : [0xffffffece769b3a8] string+0x50/0x10c
lr : [0xffffffece769ac88] vsnprintf+0x468/0x69c
...
 Call trace:
  string+0x50/0x10c
  vsnprintf+0x468/0x69c
  seq_printf+0x8c/0xd8
  print_name+0x64/0xf4
  lc_show+0xb8/0x128
  seq_read_iter+0x3cc/0x5fc
  proc_reg_read_iter+0xdc/0x1d4

The cause of the problem is the function lock_chain_get_class() will
shift lock_classes index by 1, but the index don't need to be shifted
anymore since commit 01bb6f0af992 ("locking/lockdep: Change the range
of class_idx in held_lock struct") already change the index to start
from 0.

The lock_classes[-1] located at chain_hlocks array. When printing
lock_classes[-1] after the chain_hlocks entries are modified, the
exception happened.

The output of lockdep_chains are incorrect due to this problem too.

Fixes: f611e8cf98ec ("lockdep: Take read/write status in consideration when generate chainkey")
Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20220210105011.21712-1-cheng-jui.wang@mediatek.com
---
 kernel/locking/lockdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4a882f8..f8a0212 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3462,7 +3462,7 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 	u16 chain_hlock = chain_hlocks[chain->base + i];
 	unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
 
-	return lock_classes + class_idx - 1;
+	return lock_classes + class_idx;
 }
 
 /*
@@ -3530,7 +3530,7 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 		hlock_id = chain_hlocks[chain->base + i];
 		chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
-		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
+		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
 		printk("\n");
 	}
 }