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From:   Dmitry Safonov <0x7f454c46@gmail.com>
Date:   Thu, 21 Nov 2019 22:58:21 +0000
Message-ID: <CAJwJo6bu0Hkmneg=DuwN=v_G4pkm1JQnUWKEVcudJD5L0pjLiw@mail.gmail.com>
Subject: Re: [PATCH] ACPI: only free map once in osl.c
To:     Francesco Ruggeri <fruggeri@arista.com>
Cc:     lenb@kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        open list <linux-kernel@vger.kernel.org>,
        linux-acpi@vger.kernel.org
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On Wed, 20 Nov 2019 at 05:50, Francesco Ruggeri <fruggeri@arista.com> wrote:
>
> acpi_os_map_cleanup checks map->refcount outside of acpi_ioremap_lock
> before freeing the map. This creates a race condition the can result
> in the map being freed more than once.
> A panic can be caused by running
>
> for ((i=0; i<10; i++))
> do
>         for ((j=0; j<100000; j++))
>         do
>                 cat /sys/firmware/acpi/tables/data/BERT >/dev/null
>         done &
> done
>
> This patch makes sure that only the process that drops the reference
> to 0 does the freeing.
>
> Fixes: b7c1fadd6c2e ("ACPI: Do not use krefs under a mutex in osl.c")
> Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>

Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>

Thanks,
             Dmitry