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update Documentation/filesystems/Locking for 2.6.27 changes
In the 2.6.27 circle ->fasync lost the BKL, and the last remaining
->open variant that takes the BKL is also gone. ->get_sb and ->kill_sb
didn't have BKL forever, so updated the entries while we're at that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
authored by
Christoph Hellwig
and committed by
Linus Torvalds
adaae721
82a28c79
+4
-11
+4
-11
Documentation/filesystems/Locking
+4
-11
Documentation/filesystems/Locking
···
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void (*kill_sb) (struct super_block *);
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locking rules:
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may block BKL
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-
get_sb yes yes
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-
kill_sb yes yes
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+
get_sb yes no
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+
kill_sb yes no
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->get_sb() returns error or 0 with locked superblock attached to the vfsmount
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(exclusive on ->s_umount).
···
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unlocked_ioctl: no (see below)
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compat_ioctl: no
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mmap: no
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-
open: maybe (see below)
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+
open: no
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flush: no
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release: no
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fsync: no (see below)
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aio_fsync: no
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-
fasync: yes (see below)
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+
fasync: no
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lock: yes
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readv: no
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writev: no
···
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For many filesystems, it is probably safe to acquire the inode
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semaphore. Note some filesystems (i.e. remote ones) provide no
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protection for i_size so you will need to use the BKL.
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->open() locking is in-transit: big lock partially moved into the methods.
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The only exception is ->open() in the instances of file_operations that never
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end up in ->i_fop/->proc_fops, i.e. ones that belong to character devices
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(chrdev_open() takes lock before replacing ->f_op and calling the secondary
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method. As soon as we fix the handling of module reference counters all
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instances of ->open() will be called without the BKL.
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Note: ext2_release() was *the* source of contention on fs-intensive
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loads and dropping BKL on ->release() helps to get rid of that (we still