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

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Message-ID: <20250215172440.GS1615191@kernel.org>
Date: Sat, 15 Feb 2025 17:24:40 +0000
From: Simon Horman <horms@...nel.org>
To: Purva Yeshi <purvayeshi550@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	skhan@...uxfoundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Kuniyuki Iwashima <kuniyu@...zon.com>,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH net-next v2] af_unix: Fix undefined 'other' error

+ 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@...il.com>
> ---
> V1 - https://lore.kernel.org/lkml/20250209184355.16257-1-purvayeshi550@gmail.com/
> 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.