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Commit 866707fc authored by Jan Blunck's avatar Jan Blunck Committed by Linus Torvalds
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Documentation/filesystems/Locking: update documentation on llseek() wrt BKL 



The inode's i_size is not protected by the big kernel lock.  Therefore it
does not make sense to recommend taking the BKL in filesystems llseek
operations.  Instead it should use the inode's mutex or use just use
i_size_read() instead.  Add a note that this is not protecting
file->f_pos.

Signed-off-by: default avatarJan Blunck <jblunck@suse.de>
Acked-by: default avatarAlan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ca572727

Documentation/filesystems/Locking

+3 −2
Original line number Original line Diff line number Diff line
@@ -429,8 +429,9 @@ check_flags: no 
implementations.  If your fs is not using generic_file_llseek, you

implementations.  If your fs is not using generic_file_llseek, you

need to acquire and release the appropriate locks in your ->llseek().

need to acquire and release the appropriate locks in your ->llseek().

For many filesystems, it is probably safe to acquire the inode

For many filesystems, it is probably safe to acquire the inode

mutex.  Note some filesystems (i.e. remote ones) provide no

mutex or just to use i_size_read() instead.

protection for i_size so you will need to use the BKL.

Note: this does not protect the file->f_pos against concurrent modifications

since this is something the userspace has to take care about.





Note: ext2_release() was *the* source of contention on fs-intensive

Note: ext2_release() was *the* source of contention on fs-intensive

loads and dropping BKL on ->release() helps to get rid of that (we still

loads and dropping BKL on ->release() helps to get rid of that (we still