Re: [PATCH net-next v2] af_unix: Fix undefined 'other' error

[Simon Horman]

+ Iwashima-san, Dan

On Mon, Feb 10, 2025 at 01:20:06PM +0530, Purva Yeshi wrote:
> Fix issue detected by smatch tool:
> An "undefined 'other'" error occur in __releases() annotation.
> 
> Fix an undefined 'other' error in unix_wait_for_peer() caused by  
> __releases(&unix_sk(other)->lock) being placed before 'other' is in  
> scope. Since AF_UNIX does not use Sparse annotations, remove it to fix  
> the issue.  
> 
> Eliminate the error without affecting functionality.  
> 
> Signed-off-by: Purva Yeshi <purvayeshi550@xxxxxxxxx>
> ---
> V1 - https://lore.kernel.org/lkml/20250209184355.16257-1-purvayeshi550@xxxxxxxxx/
> V2 - Remove __releases() annotation as AF_UNIX does not use Sparse annotations.

Hi Iwashima-san, all,

in v1 of this change you commented that:

  Tweaking an annotation with a comment for a static analyzer to fix
  a warning for yet another static analyzer is too much.

  Please remove sparse annotation instead.

  Here's the only place where sparse is used in AF_UNIX code, and we
  don't use sparse even for /proc/net/unix.

And I do understand entirely that we don't want to overly tweak
things to keep static analysis tools happy. But I don't think the
patch description describes the situation completely. So I'd like
to provide a bit more information.

My understanding is that the two static analysis tools under discussion
are Smatch and Sparse, where AFAIK Smatch is a fork of Sparse.

Without this patch, when checking af_unix.c, both Smatch and Sparse report
(only):

 .../af_unix.c:1511:9: error: undefined identifier 'other'
 .../af_unix.c:1511:9: error: undefined identifier 'other'
 .../af_unix.c:1511:9: error: undefined identifier 'other'
 .../af_unix.c:1511:9: error: undefined identifier 'other'

And with either v1 or v2 of this patch applied Smatch reports nothing.
While Sparse reports:

 .../af_unix.c:234:13: warning: context imbalance in 'unix_table_double_lock' - wrong count at exit
 .../af_unix.c:253:28: warning: context imbalance in 'unix_table_double_unlock' - unexpected unlock
 .../af_unix.c:1386:13: warning: context imbalance in 'unix_state_double_lock' - wrong count at exit
 .../af_unix.c:1403:17: warning: context imbalance in 'unix_state_double_unlock' - unexpected unlock
 .../af_unix.c:2089:25: warning: context imbalance in 'unix_dgram_sendmsg' - unexpected unlock
 .../af_unix.c:3335:20: warning: context imbalance in 'unix_get_first' - wrong count at exit
 .../af_unix.c:3366:34: warning: context imbalance in 'unix_get_next' - unexpected unlock
 .../af_unix.c:3396:42: warning: context imbalance in 'unix_seq_stop' - unexpected unlock
 .../af_unix.c:3499:34: warning: context imbalance in 'bpf_iter_unix_hold_batch' - unexpected unlock

TBH, I'm unsure which is worse. Nor how to improve things.