linux-kernel - Re: [tip: perf/urgent] perf/aux: Fix tracking of auxiliary trace buffer allocation

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Date:   Fri, 15 Nov 2019 18:06:59 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     tip-bot2 for Thomas Richter <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org
Cc:     Thomas Richter <tmricht@...ux.ibm.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, acme@...nel.org,
        gor@...ux.ibm.com, hechaol@...com, heiko.carstens@...ibm.com,
        linux-perf-users@...r.kernel.org, songliubraving@...com,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com
Subject: Re: [tip: perf/urgent] perf/aux: Fix tracking of auxiliary trace buffer allocation

"tip-bot2 for Thomas Richter" <tip-bot2@...utronix.de> writes:

>  		/* now it's safe to free the pages */
> -		atomic_long_sub(rb->aux_nr_pages, &mmap_user->locked_vm);
> -		atomic64_sub(rb->aux_mmap_locked, &vma->vm_mm->pinned_vm);
> +		if (!rb->aux_mmap_locked)
> +			atomic_long_sub(rb->aux_nr_pages, &mmap_user->locked_vm);
> +		else
> +			atomic64_sub(rb->aux_mmap_locked, &vma->vm_mm->pinned_vm);

This only works correctly when rb->aux_mmap_locked is either equal to
rb->aux_nr_pages or zero. Otherwise, it leaks

  rb->aux_nr_pages - rb->aux_mmap_locked

in the locked_vm permanently.

Regards,
--
Alex