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btrfs: ensure fiemap doesn't race with writes when FIEMAP_FLAG_SYNC i…
…s given [ Upstream commit 418b090 ] When FIEMAP_FLAG_SYNC is given to fiemap the expectation is that that are no concurrent writes and we get a stable view of the inode's extent layout. When the flag is given we flush all IO (and wait for ordered extents to complete) and then lock the inode in shared mode, however that leaves open the possibility that a write might happen right after the flushing and before locking the inode. So fix this by flushing again after locking the inode - we leave the initial flushing before locking the inode to avoid holding the lock and blocking other RO operations while waiting for IO and ordered extents to complete. The second flushing while holding the inode's lock will most of the time do nothing or very little since the time window for new writes to have happened is small. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> Stable-dep-of: 978b63f ("btrfs: fix race when detecting delalloc ranges during fiemap") Signed-off-by: Sasha Levin <sashal@kernel.org>
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