linux-kernel - Re: [PATCH 2/2] perf lock: Don't free "lock_seq_stat" if read

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Date:   Wed, 21 Oct 2020 08:42:23 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf lock: Don't free "lock_seq_stat" if read_count
 isn't zero

Hi all,

On Wed, Oct 21, 2020 at 08:26:19AM +0800, Leo Yan wrote:
> When execute command "perf lock report", it hits failure and outputs log
> as follows:
> 
>   perf: builtin-lock.c:623: report_lock_release_event: Assertion `!(seq->read_count < 0)' failed.
>   Aborted
> 
> This is an imbalance issue.  The locking sequence structure
> "lock_seq_stat" contains the reader counter and it is used to check if
> the locking sequence is balance or not between acquiring and releasing.
> 
> If the tool wrongly frees "lock_seq_stat" when "read_count" isn't zero,
> the "read_count" will be reset to zero when allocate a new structure at
> the next time; thus it causes the wrong counting for reader and finally
> results in imbalance issue.
> 
> To fix this issue, if detects "read_count" is not zero (means still
> have read user in the locking sequence), goto the "end" tag to skip
> freeing structure "lock_seq_stat".

Please ignore this patch set and directly to review patch set v2; I
forgot adding "fixes" tag in this patch, so updated in patch set v2.

Sorry for spamming.

Leo