From: Johannes Thumshirn <jthumshirn@suse.de>
To: Omar Sandoval <osandov@osandov.com>
Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 4/7] btrfs: don't prematurely free work in reada_start_machine_worker()
Date: Tue, 17 Sep 2019 14:09:48 +0200 [thread overview]
Message-ID: <20190917120948.GD12128@x250> (raw)
In-Reply-To: <15b3aebf569f2a2831bc852789935fae37798f8d.1568658527.git.osandov@fb.com>
On Mon, Sep 16, 2019 at 11:30:55AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
>
> Currently, reada_start_machine_worker() frees the reada_machine_work and
> then calls __reada_start_machine() to do readahead. This is another
> potential instance of the bug in "btrfs: don't prematurely free work in
> run_ordered_work()".
>
> There _might_ already be a deadlock here: reada_start_machine_worker()
> can depend on itself through stacked filesystems (__read_start_machine()
> -> reada_start_machine_dev() -> reada_tree_block_flagged() ->
> read_extent_buffer_pages() -> submit_one_bio() ->
> btree_submit_bio_hook() -> btrfs_map_bio() -> submit_stripe_bio() ->
> submit_bio() onto a loop device can trigger readahead on the lower
> filesystem).
>
> Either way, let's fix it by freeing the work at the end.
Also remove the local fs_info variable as it got obsolete.
Anyways,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
--
Johannes Thumshirn SUSE Labs Filesystems
jthumshirn@suse.de +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850
next prev parent reply other threads:[~2019-09-17 12:09 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-16 18:30 [PATCH 0/7] btrfs: workqueue fixes+cleanups Omar Sandoval
2019-09-16 18:30 ` [PATCH 1/7] btrfs: get rid of unnecessary memset() of work item Omar Sandoval
2019-09-17 11:46 ` Johannes Thumshirn
2019-09-16 18:30 ` [PATCH 2/7] btrfs: don't prematurely free work in run_ordered_work() Omar Sandoval
2019-09-17 12:04 ` Johannes Thumshirn
2019-09-16 18:30 ` [PATCH 3/7] btrfs: don't prematurely free work in end_workqueue_fn() Omar Sandoval
2019-09-17 12:05 ` Johannes Thumshirn
2019-09-16 18:30 ` [PATCH 4/7] btrfs: don't prematurely free work in reada_start_machine_worker() Omar Sandoval
2019-09-17 12:09 ` Johannes Thumshirn [this message]
2019-09-16 18:30 ` [PATCH 5/7] btrfs: don't prematurely free work in scrub_missing_raid56_worker() Omar Sandoval
2019-09-17 12:10 ` Johannes Thumshirn
2019-09-16 18:30 ` [PATCH 6/7] btrfs: get rid of unique workqueue helper functions Omar Sandoval
2019-09-16 18:30 ` [PATCH 7/7] btrfs: get rid of pointless wtag variable in async-thread.c Omar Sandoval
2019-09-24 14:45 ` [PATCH 0/7] btrfs: workqueue fixes+cleanups David Sterba
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