Andi Kleen ef3d0fd27e vfs: do (nearly) lockless generic_file_llseek ... The i_mutex lock use of generic _file_llseek hurts. Independent processes accessing the same file synchronize over a single lock, even though they have no need for synchronization at all. Under high utilization this can cause llseek to scale very poorly on larger systems. This patch does some rethinking of the llseek locking model: First the 64bit f_pos is not necessarily atomic without locks on 32bit systems. This can already cause races with read() today. This was discussed on linux-kernel in the past and deemed acceptable. The patch does not change that. Let's look at the different seek variants: SEEK_SET: Doesn't really need any locking. If there's a race one writer wins, the other loses. For 32bit the non atomic update races against read() stay the same. Without a lock they can also happen against write() now. The read() race was deemed acceptable in past discussions, and I think if it's ok for read it's ok for write too. => Don't need a lock. SEEK_END: This behaves like SEEK_SET plus it reads the maximum size too. Reading the maximum size would have the 32bit atomic problem. But luckily we already have a way to read the maximum size without locking (i_size_read), so we can just use that instead. Without i_mutex there is no synchronization with write() anymore, however since the write() update is atomic on 64bit it just behaves like another racy SEEK_SET. On non atomic 32bit it's the same as SEEK_SET. => Don't need a lock, but need to use i_size_read() SEEK_CUR: This has a read-modify-write race window on the same file. One could argue that any application doing unsynchronized seeks on the same file is already broken. But for the sake of not adding a regression here I'm using the file->f_lock to synchronize this. Using this lock is much better than the inode mutex because it doesn't synchronize between processes. => So still need a lock, but can use a f_lock. This patch implements this new scheme in generic_file_llseek. I dropped generic_file_llseek_unlocked and changed all callers. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Christoph Hellwig <hch@lst.de>		2011-10-28 14:58:58 +02:00
..
9p	fs/9p: Use protocol-defined value for lock/getlock 'type' field.	2011-09-06 08:17:16 -05:00
adfs
affs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
afs	AFS: Fix silly characters in a comment	2011-07-20 20:48:03 -04:00
autofs4	autofs4: fix debug printk warning uncovered by cleanup	2011-08-08 12:02:43 -07:00
befs	befs: Validate length of long symbolic links.	2011-08-17 13:31:24 -07:00
bfs	bfs: remove unnecessary dentry_unhash on dir rename	2011-05-28 01:02:50 -04:00
btrfs	vfs: do (nearly) lockless generic_file_llseek	2011-10-28 14:58:58 +02:00
cachefiles	kill useless checks for sb->s_op == NULL	2011-07-20 01:44:21 -04:00
ceph	Merge branch 'for-linus' of git://ceph.newdream.net/git/ceph-client	2011-09-09 15:48:34 -07:00
cifs	vfs: do (nearly) lockless generic_file_llseek	2011-10-28 14:58:58 +02:00
coda	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
configfs	configfs: remove unnecessary dentry_unhash on rmdir, dir rename	2011-05-28 01:02:54 -04:00
cramfs	cramfs: get_cramfs_inode() returns ERR_PTR() on failure	2011-07-17 23:22:02 -04:00
debugfs	debugfs: move to new strtobool	2011-05-19 16:55:28 +09:30
devpts
dlm	Merge branch 'for-3.1' of git://linux-nfs.org/~bfields/linux	2011-07-25 22:49:19 -07:00
ecryptfs	Ecryptfs: Add mount option to check uid of device being mounted = expect uid	2011-08-09 23:29:01 -05:00
efs	make d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err)	2011-07-20 01:44:26 -04:00
exofs	Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd	2011-08-06 22:56:03 -07:00
exportfs
ext2	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6	2011-08-01 13:48:31 -10:00
ext3	block: separate priority boosting from REQ_META	2011-08-23 14:50:29 +02:00
ext4	Merge branch 'for-linus' of git://git.kernel.dk/linux-block	2011-09-21 13:20:21 -07:00
fat	Merge git://git.kernel.org/pub/scm/linux/kernel/git/hirofumi/fatfs-2.6	2011-08-18 14:16:13 -07:00
freevxfs	treewide: fix a few typos in comments	2011-05-10 10:16:21 +02:00
fscache	FS-Cache: Fix __fscache_uncache_all_inode_pages()'s outer loop	2011-07-21 10:59:16 -07:00
fuse	fuse: fix memory leak	2011-09-12 11:47:10 -07:00
gfs2	vfs: do (nearly) lockless generic_file_llseek	2011-10-28 14:58:58 +02:00
hfs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
hfsplus	hfsplus: fix filesystem size checks	2011-09-15 09:03:17 -07:00
hostfs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
hpfs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
hppfs	hppfs: missing include	2011-07-27 22:21:58 -04:00
hugetlbfs	lockdep: Add helper function for dir vs file i_mutex annotation	2011-08-25 10:50:18 -07:00
isofs	isofs: Remove global fs lock	2011-07-22 19:42:12 -04:00
jbd	jbd: Use WRITE_SYNC in journal checkpoint.	2011-06-28 00:06:41 +02:00
jbd2	jbd2: remove jbd2_dev_to_name() from jbd2 tracepoints	2011-07-10 22:05:08 -04:00
jffs2	switch posix_acl_equiv_mode() to umode_t *	2011-08-01 02:10:06 -04:00
jfs	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/shaggy/jfs-2.6	2011-08-15 08:40:24 -07:00
lockd	Merge branch 'nfs-for-3.1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs	2011-07-27 13:23:02 -07:00
logfs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
minix	minix_getattr(): don't bother with ->d_parent	2011-07-20 20:47:53 -04:00
ncpfs	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
nfs	vfs: do (nearly) lockless generic_file_llseek	2011-10-28 14:58:58 +02:00
nfs_common
nfsd	Merge branch 'for-3.1' of git://linux-nfs.org/~bfields/linux	2011-07-25 22:49:19 -07:00
nilfs2	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
nls
notify	atomic: use <linux/atomic.h>	2011-07-26 16:49:47 -07:00
ntfs	atomic: use <linux/atomic.h>	2011-07-26 16:49:47 -07:00
ocfs2	switch posix_acl_equiv_mode() to umode_t *	2011-08-01 02:10:06 -04:00
omfs	omfs: fix (mode & S_IFDIR) abuse	2011-07-26 13:05:28 -04:00
openpromfs
partitions	Merge branch 'for-linus' into for-3.1/core	2011-07-01 16:17:13 +02:00
proc	teach /proc/$pid/numa_maps about transparent hugepages	2011-09-21 13:15:44 -07:00
pstore	pstore: Allow the user to explicitly choose a backend	2011-07-22 16:14:39 -07:00
qnx4
quota	VFS: Fix the remaining automounter semantics regressions	2011-09-26 19:16:46 -07:00
ramfs	ramfs: fix memleak on no-mmu arch	2011-04-14 16:06:56 -07:00
reiserfs	switch posix_acl_equiv_mode() to umode_t *	2011-08-01 02:10:06 -04:00
romfs	romfs: fix romfs_get_unmapped_area() argument check	2011-06-27 18:00:12 -07:00
squashfs	Merge git://git.kernel.org/pub/scm/linux/kernel/git/pkl/squashfs-linus	2011-07-25 22:50:35 -07:00
sysfs	->permission() sanitizing: don't pass flags to ->permission()	2011-07-20 01:43:24 -04:00
sysv	sysv: remove unnecessary dentry_unhash from rmdir, dir rename	2011-05-28 01:02:50 -04:00
ubifs	UBIFS: not build debug messages with CONFIG_UBIFS_FS_DEBUG disabled	2011-08-19 18:58:58 +03:00
udf	switch udf_ioctl() to inode_permission()	2011-07-20 01:43:07 -04:00
ufs	make d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err)	2011-07-20 01:44:26 -04:00
xfs	xfs: revert to using a kthread for AIL pushing	2011-10-11 11:02:49 -05:00
aio.c
anon_inodes.c	vfs: dont chain pipe/anon/socket on superblock s_inodes list	2011-07-26 12:57:09 -04:00
attr.c	fs: move inode_dio_wait calls into ->setattr	2011-07-20 20:47:47 -04:00
bad_inode.c	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
binfmt_aout.c
binfmt_elf_fdpic.c	consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling	2011-07-20 01:43:10 -04:00
binfmt_elf.c	consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling	2011-07-20 01:43:10 -04:00
binfmt_em86.c
binfmt_flat.c	CRED: Fix load_flat_shared_library() to initialise bprm correctly	2011-05-03 10:10:51 +10:00
binfmt_misc.c	consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling	2011-07-20 01:43:10 -04:00
binfmt_script.c
binfmt_som.c
bio-integrity.c
bio.c	block: improve the bio_add_page() and bio_add_pc_page() descriptions	2011-05-28 14:44:46 +02:00
block_dev.c	Avoid dereferencing a 'request_queue' after last close.	2011-09-10 17:20:21 +10:00
buffer.c	cleanup: vfs: small comment fix for block_invalidatepage	2011-10-28 13:55:08 +02:00
char_dev.c
compat_binfmt_elf.c
compat_ioctl.c	compat_ioctl: add compat handler for PPPIOCGL2TPSTATS	2011-08-07 22:24:41 -07:00
compat.c	compat: sync compat_stats with statfs.	2011-10-28 14:58:53 +02:00
dcache.c	vfs: renumber DCACHE_xyz flags, remove some stale ones	2011-08-06 22:52:40 -07:00
dcookies.c	oprofile, dcookies: Fix possible circular locking dependency	2011-05-31 16:33:35 +02:00
direct-io.c	direct-io: merge direct_io_walker into __blockdev_direct_IO	2011-10-28 14:58:58 +02:00
drop_caches.c	vmscan: change shrinker API by passing shrink_control struct	2011-05-25 08:39:26 -07:00
eventfd.c
eventpoll.c	atomic: use <linux/atomic.h>	2011-07-26 16:49:47 -07:00
exec.c	move RLIMIT_NPROC check from set_user() to do_execve_common()	2011-08-11 11:24:42 -07:00
fcntl.c
fhandle.c	fs/fhandle.c: add <linux/personality.h> for ia64	2011-04-14 16:06:56 -07:00
fifo.c
file_table.c	atomic: use <linux/atomic.h>	2011-07-26 16:49:47 -07:00
file.c	vfs: avoid large kmalloc()s for the fdtable	2011-04-28 11:28:20 -07:00
filesystems.c	fs: synchronize_rcu when unregister_filesystem success not failure	2011-04-17 10:42:01 -07:00
fs_struct.c
fs-writeback.c	don't busy retry the inode on failed grab_super_passive()	2011-07-31 22:52:08 +08:00
generic_acl.c	switch posix_acl_equiv_mode() to umode_t *	2011-08-01 02:10:06 -04:00
inode.c	vfs: fix spinning prevention in prune_icache_sb	2011-10-28 14:58:55 +02:00
internal.h	superblock: move pin_sb_for_writeback() to fs/super.c	2011-07-20 01:44:38 -04:00
ioctl.c
ioprio.c
Kconfig	tmpfs: expand "help" to explain value of TMPFS_POSIX_ACL	2011-08-03 14:25:25 -10:00
Kconfig.binfmt
libfs.c	fix IN_DELETE_SELF on overwriting rename() on ramfs et.al.	2011-07-22 19:42:11 -04:00
locks.c	locks: rename lock-manager ops	2011-07-20 20:23:19 -04:00
Makefile	nfsd: Remove deprecated nfsctl system call and related code.	2011-07-15 18:58:42 -04:00
mbcache.c	vmscan: change shrinker API by passing shrink_control struct	2011-05-25 08:39:26 -07:00
mpage.c	mm/fs: add hooks to support cleancache	2011-05-26 10:01:43 -06:00
namei.c	vfs: add a comment to inode_permission()	2011-10-28 14:58:55 +02:00
namespace.c	vfs: add "device" tag to /proc/self/mountstats	2011-10-28 13:55:08 +02:00
no-block.c
open.c	merge fchmod() and fchmodat() guts, kill ancient broken kludge	2011-07-26 15:07:43 -04:00
pipe.c	vfs: dont chain pipe/anon/socket on superblock s_inodes list	2011-07-26 12:57:09 -04:00
pnode.c
pnode.h
posix_acl.c	vfs: pass all mask flags check_acl and posix_acl_permission	2011-10-28 14:58:54 +02:00
read_write.c	vfs: do (nearly) lockless generic_file_llseek	2011-10-28 14:58:58 +02:00
read_write.h
readdir.c
select.c
seq_file.c
signalfd.c
splice.c	tmpfs: clone shmem_file_splice_read()	2011-07-25 20:57:11 -07:00
stack.c	mm: a few small updates for radix-swap	2011-08-03 14:25:24 -10:00
stat.c	vfs: remove LOOKUP_NO_AUTOMOUNT flag	2011-09-27 08:12:33 -07:00
statfs.c
super.c	Merge branch 'for-3.1/core' of git://git.kernel.dk/linux-block	2011-07-25 10:33:36 -07:00
sync.c	fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers	2011-07-20 20:47:59 -04:00
timerfd.c	timerfd: Fix wakeup of processes when timer is cancelled on clock change	2011-06-14 11:46:14 +02:00
utimes.c
xattr_acl.c
xattr.c	Cache xattr security drop check for write v2	2011-05-28 12:02:09 -04:00