From: Joel Fernandes <joel@joelfernandes.org>
To: Suren Baghdasaryan <surenb@google.com>
Cc: "open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
hdanton@sina.com, kernel-team <kernel-team@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
"Michal Hocko" <mhocko@kernel.org>,
ebiggers@kernel.org, linux-mm <linux-mm@kvack.org>,
"Arve Hjønnevåg" <arve@android.com>,
"Hridya Valsaraju" <hridya@google.com>,
"Martijn Coenen" <maco@android.com>,
"Christian Brauner" <christian@brauner.io>
Subject: Re: [PATCH 1/1] staging: android: ashmem: Fix lockdep warning for write operation
Date: Wed, 29 Jul 2020 23:23:55 -0400 [thread overview]
Message-ID: <CAEXW_YTps99nspdCtvMi6hO7kbpz8PgOH--g4d2-8gticrs4OQ@mail.gmail.com> (raw)
In-Reply-To: <20200716024527.4009170-1-surenb@google.com>
On Wed, Jul 15, 2020 at 10:45 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> syzbot report [1] describes a deadlock when write operation against an
> ashmem fd executed at the time when ashmem is shrinking its cache results
> in the following lock sequence:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(fs_reclaim);
> lock(&sb->s_type->i_mutex_key#13);
> lock(fs_reclaim);
> lock(&sb->s_type->i_mutex_key#13);
>
> kswapd takes fs_reclaim and then inode_lock while generic_perform_write
> takes inode_lock and then fs_reclaim. However ashmem does not support
> writing into backing shmem with a write syscall. The only way to change
> its content is to mmap it and operate on mapped memory. Therefore the race
> that lockdep is warning about is not valid. Resolve this by introducing a
> separate lockdep class for the backing shmem inodes.
>
> [1]: https://lkml.kernel.org/lkml/0000000000000b5f9d059aa2037f@google.com/
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
Once Eric's nits are resolved:
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Thanks.
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next prev parent reply other threads:[~2020-07-30 3:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 2:45 [PATCH 1/1] staging: android: ashmem: Fix lockdep warning for write operation Suren Baghdasaryan
2020-07-16 3:30 ` Eric Biggers
2020-07-16 19:30 ` Suren Baghdasaryan
2020-07-30 3:23 ` Joel Fernandes [this message]
2020-07-30 19:15 ` Suren Baghdasaryan
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