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authorJan Blunck <jblunck@suse.de>2010-05-26 14:44:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-27 09:12:56 -0700
commit866707fc2721df8fee637fcf0239628b9231f9ea (patch)
tree485b1a369c1b879a2dd556e44bd30a23e6bfd87f /Documentation
parentca572727dbb945e443564029a495157fd2e72995 (diff)
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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: Jan Blunck <jblunck@suse.de> Acked-by: Alan 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/Locking5
1 files changed, 3 insertions, 2 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index af1608070cd..61c98f03baa 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -429,8 +429,9 @@ check_flags: no
implementations. If your fs is not using generic_file_llseek, you
need to acquire and release the appropriate locks in your ->llseek().
For many filesystems, it is probably safe to acquire the inode
-mutex. Note some filesystems (i.e. remote ones) provide no
-protection for i_size so you will need to use the BKL.
+mutex or just to use i_size_read() instead.
+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
loads and dropping BKL on ->release() helps to get rid of that (we still