The patch titled
Documentation/filesystems/Locking: update documentation on llseek() wrt BKL
has been added to the -mm tree. Its filename is
documentation-filesystems-locking-update-documentation-on-llseek-wrt-bkl.patch
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Subject: Documentation/filesystems/Locking: update documentation on llseek() wrt BKL
From: Jan Blunck <jblunck@xxxxxxx>
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@xxxxxxx>
Acked-by: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/Locking | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN Documentation/filesystems/Locking~documentation-filesystems-locking-update-documentation-on-llseek-wrt-bkl Documentation/filesystems/Locking
--- a/Documentation/filesystems/Locking~documentation-filesystems-locking-update-documentation-on-llseek-wrt-bkl
+++ a/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
-semaphore. 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
_
Patches currently in -mm which might be from jblunck@xxxxxxx are
osst-update-ppos-instead-of-using-file-f_pos.patch
drivers-sbus-char-flashc-flash_read-should-update-ppos-instead-of-file-f_pos.patch
arch-cris-arch-v10-drivers-eepromc-eeprom_read-eeprom_write-should-update-ppos-instead-of-file-f_pos.patch
frv-remove-struct-file-argument-from-sysctl-proc_handler.patch
misdn-remove-unnecessary-test-on-f_pos.patch
zcrypt-use-nonseekable_open.patch
rtc-m41t80-use-nonseekable_open.patch
vfs-introduce-noop_llseek.patch
osst-use-noop_llseek-instead-of-default_llseek.patch
st-use-noop_llseek-instead-of-default_llseek.patch
fs-do-not-fallback-to-default_llseek-when-readdir-uses-bkl.patch
documentation-filesystems-locking-update-documentation-on-llseek-wrt-bkl.patch
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