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13 July 2024, 08:20:57 UTC
Revision f82c458a2c3ffb94b431fc6ad791a79df1b3713e authored by Chris Mason on 19 November 2014, 18:25:09 UTC, committed by Chris Mason on 19 November 2014, 18:34:35 UTC 
btrfs: fix lockups from btrfs_clear_path_blocking
 
The fair reader/writer locks mean that btrfs_clear_path_blocking needs
to strictly follow lock ordering rules even when we already have
blocking locks on a given path.

Before we can clear a blocking lock on the path, we need to make sure
all of the locks have been converted to blocking.  This will remove lock
inversions against anyone spinning in write_lock() against the buffers
we're trying to get read locks on.  These inversions didn't exist before
the fair read/writer locks, but now we need to be more careful.

We papered over this deadlock in the past by changing
btrfs_try_read_lock() to be a true trylock against both the spinlock and
the blocking lock.  This was slower, and not sufficient to fix all the
deadlocks.  This patch adds a btrfs_tree_read_lock_atomic(), which
basically means get the spinlock but trylock on the blocking lock.

Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reported-by: Patrick Schmid <schmid@phys.ethz.ch>
cc: stable@vger.kernel.org #v3.15+
1 parent 6e5aafb
History
Tip revision: f82c458a2c3ffb94b431fc6ad791a79df1b3713e authored by Chris Mason on 19 November 2014, 18:25:09 UTC
btrfs: fix lockups from btrfs_clear_path_blocking
Tip revision: f82c458
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