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update Documentation/filesystems/Locking

Browse source 
Mostly inspired by all the recent BKL removal changes, but a lot of older
updates also weren't properly recorded.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Christoph Hellwig 2010-12-16 12:04:54 +01:00 committed by Linus Torvalds
parent 4ef9e11d68
commit b83be6f20a
1 changed files with 101 additions and 111 deletions
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212
Documentation/filesystems/Locking
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@ -18,7 +18,6 @@ prototypes:
char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
locking rules:
none have BKL
dcache_lock rename_lock ->d_lock may block
d_revalidate: no no no yes
d_hash no no no yes
@ -42,18 +41,23 @@ ata *);
int (*rename) (struct inode *, struct dentry *,
struct inode *, struct dentry *);
int (*readlink) (struct dentry *, char __user *,int);
int (*follow_link) (struct dentry *, struct nameidata *);
void * (*follow_link) (struct dentry *, struct nameidata *);
void (*put_link) (struct dentry *, struct nameidata *, void *);
void (*truncate) (struct inode *);
int (*permission) (struct inode *, int, struct nameidata *);
int (*check_acl)(struct inode *, int);
int (*setattr) (struct dentry *, struct iattr *);
int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
ssize_t (*listxattr) (struct dentry *, char *, size_t);
int (*removexattr) (struct dentry *, const char *);
void (*truncate_range)(struct inode *, loff_t, loff_t);
long (*fallocate)(struct inode *inode, int mode, loff_t offset, loff_t len);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
locking rules:
all may block, none have BKL
all may block
i_mutex(inode)
lookup: yes
create: yes
@ -66,19 +70,24 @@ rmdir: yes (both) (see below)
rename: yes (all) (see below)
readlink: no
follow_link: no
put_link: no
truncate: yes (see below)
setattr: yes
permission: no
check_acl: no
getattr: no
setxattr: yes
getxattr: no
listxattr: no
removexattr: yes
truncate_range: yes
fallocate: no
fiemap: no
Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
victim.
cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
->truncate() is never called directly - it's a callback, not a
method. It's called by vmtruncate() - library function normally used by
method. It's called by vmtruncate() - deprecated library function used by
->setattr(). Locking information above applies to that call (i.e. is
inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
passed).
@ -91,7 +100,7 @@ prototypes:
struct inode *(*alloc_inode)(struct super_block *sb);
void (*destroy_inode)(struct inode *);
void (*dirty_inode) (struct inode *);
int (*write_inode) (struct inode *, int);
int (*write_inode) (struct inode *, struct writeback_control *wbc);
int (*drop_inode) (struct inode *);
void (*evict_inode) (struct inode *);
void (*put_super) (struct super_block *);
@ -105,10 +114,11 @@ prototypes:
int (*show_options)(struct seq_file *, struct vfsmount *);
ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
int (*trim_fs) (struct super_block *, struct fstrim_range *);
locking rules:
All may block [not true, see below]
None have BKL
s_umount
alloc_inode:
destroy_inode:
@ -127,6 +137,8 @@ umount_begin: no
show_options: no (namespace_sem)
quota_read: no (see below)
quota_write: no (see below)
bdev_try_to_free_page: no (see below)
trim_fs: no
->statfs() has s_umount (shared) when called by ustat(2) (native or
compat), but that's an accident of bad API; s_umount is used to pin
@ -139,19 +151,25 @@ be the only ones operating on the quota file by the quota code (via
dqio_sem) (unless an admin really wants to screw up something and
writes to quota files with quotas on). For other details about locking
see also dquot_operations section.
->bdev_try_to_free_page is called from the ->releasepage handler of
the block device inode. See there for more details.
--------------------------- file_system_type ---------------------------
prototypes:
int (*get_sb) (struct file_system_type *, int,
const char *, void *, struct vfsmount *);
struct dentry *(*mount) (struct file_system_type *, int,
const char *, void *);
void (*kill_sb) (struct super_block *);
locking rules:
may block BKL
get_sb yes no
kill_sb yes no
may block
get_sb yes
mount yes
kill_sb yes
->get_sb() returns error or 0 with locked superblock attached to the vfsmount
(exclusive on ->s_umount).
->mount() returns ERR_PTR or the root dentry.
->kill_sb() takes a write-locked superblock, does all shutdown work on it,
unlocks and drops the reference.
@ -176,27 +194,35 @@ prototypes:
void (*freepage)(struct page *);
int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
loff_t offset, unsigned long nr_segs);
int (*launder_page) (struct page *);
int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
unsigned long *);
int (*migratepage)(struct address_space *, struct page *, struct page *);
int (*launder_page)(struct page *);
int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
int (*error_remove_page)(struct address_space *, struct page *);
locking rules:
All except set_page_dirty and freepage may block
BKL PageLocked(page) i_mutex
writepage: no yes, unlocks (see below)
readpage: no yes, unlocks
sync_page: no maybe
writepages: no
set_page_dirty no no
readpages: no
write_begin: no locks the page yes
write_end: no yes, unlocks yes
perform_write: no n/a yes
bmap: no
invalidatepage: no yes
releasepage: no yes
freepage: no yes
direct_IO: no
launder_page: no yes
PageLocked(page) i_mutex
writepage: yes, unlocks (see below)
readpage: yes, unlocks
sync_page: maybe
writepages:
set_page_dirty no
readpages:
write_begin: locks the page yes
write_end: yes, unlocks yes
bmap:
invalidatepage: yes
releasepage: yes
freepage: yes
direct_IO:
get_xip_mem: maybe
migratepage: yes (both)
launder_page: yes
is_partially_uptodate: yes
error_remove_page: yes
->write_begin(), ->write_end(), ->sync_page() and ->readpage()
may be called from the request handler (/dev/loop).
@ -276,9 +302,8 @@ under spinlock (it cannot block) and is sometimes called with the page
not locked.
->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
filesystems and by the swapper. The latter will eventually go away. All
instances do not actually need the BKL. Please, keep it that way and don't
breed new callers.
filesystems and by the swapper. The latter will eventually go away. Please,
keep it that way and don't breed new callers.
->invalidatepage() is called when the filesystem must attempt to drop
some or all of the buffers from the page when it is being truncated. It
@ -299,47 +324,37 @@ cleaned, or an error value if not. Note that in order to prevent the page
getting mapped back in and redirtied, it needs to be kept locked
across the entire operation.
Note: currently almost all instances of address_space methods are
using BKL for internal serialization and that's one of the worst sources
of contention. Normally they are calling library functions (in fs/buffer.c)
and pass foo_get_block() as a callback (on local block-based filesystems,
indeed). BKL is not needed for library stuff and is usually taken by
foo_get_block(). It's an overkill, since block bitmaps can be protected by
internal fs locking and real critical areas are much smaller than the areas
filesystems protect now.
----------------------- file_lock_operations ------------------------------
prototypes:
void (*fl_insert)(struct file_lock *); /* lock insertion callback */
void (*fl_remove)(struct file_lock *); /* lock removal callback */
void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
void (*fl_release_private)(struct file_lock *);
locking rules:
BKL may block
fl_insert: yes no
fl_remove: yes no
fl_copy_lock: yes no
fl_release_private: yes yes
file_lock_lock may block
fl_copy_lock: yes no
fl_release_private: maybe no
----------------------- lock_manager_operations ---------------------------
prototypes:
int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
void (*fl_notify)(struct file_lock *); /* unblock callback */
int (*fl_grant)(struct file_lock *, struct file_lock *, int);
void (*fl_release_private)(struct file_lock *);
void (*fl_break)(struct file_lock *); /* break_lease callback */
int (*fl_mylease)(struct file_lock *, struct file_lock *);
int (*fl_change)(struct file_lock **, int);
locking rules:
BKL may block
fl_compare_owner: yes no
fl_notify: yes no
fl_release_private: yes yes
fl_break: yes no
file_lock_lock may block
fl_compare_owner: yes no
fl_notify: yes no
fl_grant: no no
fl_release_private: maybe no
fl_break: yes no
fl_mylease: yes no
fl_change yes no
Currently only NFSD and NLM provide instances of this class. None of the
them block. If you have out-of-tree instances - please, show up. Locking
in that area will change.
--------------------------- buffer_head -----------------------------------
prototypes:
void (*b_end_io)(struct buffer_head *bh, int uptodate);
@ -364,17 +379,17 @@ prototypes:
void (*swap_slot_free_notify) (struct block_device *, unsigned long);
locking rules:
BKL bd_mutex
open: no yes
release: no yes
ioctl: no no
compat_ioctl: no no
direct_access: no no
media_changed: no no
unlock_native_capacity: no no
revalidate_disk: no no
getgeo: no no
swap_slot_free_notify: no no (see below)
bd_mutex
open: yes
release: yes
ioctl: no
compat_ioctl: no
direct_access: no
media_changed: no
unlock_native_capacity: no
revalidate_disk: no
getgeo: no
swap_slot_free_notify: no (see below)
media_changed, unlock_native_capacity and revalidate_disk are called only from
check_disk_change().
@ -413,34 +428,21 @@ prototypes:
unsigned long (*get_unmapped_area)(struct file *, unsigned long,
unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
};
locking rules:
All may block.
BKL
llseek: no (see below)
read: no
aio_read: no
write: no
aio_write: no
readdir: no
poll: no
unlocked_ioctl: no
compat_ioctl: no
mmap: no
open: no
flush: no
release: no
fsync: no (see below)
aio_fsync: no
fasync: no
lock: yes
readv: no
writev: no
sendfile: no
sendpage: no
get_unmapped_area: no
check_flags: no
All may block except for ->setlease.
No VFS locks held on entry except for ->fsync and ->setlease.
->fsync() has i_mutex on inode.
->setlease has the file_list_lock held and must not sleep.
->llseek() locking has moved from llseek to the individual llseek
implementations. If your fs is not using generic_file_llseek, you
@ -450,17 +452,10 @@ 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
grab BKL for cases when we close a file that had been opened r/w, but that
can and should be done using the internal locking with smaller critical areas).
Current worst offender is ext2_get_block()...
->fasync() is called without BKL protection, and is responsible for
maintaining the FASYNC bit in filp->f_flags. Most instances call
fasync_helper(), which does that maintenance, so it's not normally
something one needs to worry about. Return values > 0 will be mapped to
zero in the VFS layer.
->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
Most instances call fasync_helper(), which does that maintenance, so it's
not normally something one needs to worry about. Return values > 0 will be
mapped to zero in the VFS layer.
->readdir() and ->ioctl() on directories must be changed. Ideally we would
move ->readdir() to inode_operations and use a separate method for directory
@ -471,8 +466,6 @@ components. And there are other reasons why the current interface is a mess...
->read on directories probably must go away - we should just enforce -EISDIR
in sys_read() and friends.
->fsync() has i_mutex on inode.
--------------------------- dquot_operations -------------------------------
prototypes:
int (*write_dquot) (struct dquot *);
@ -507,12 +500,12 @@ prototypes:
int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
locking rules:
BKL mmap_sem PageLocked(page)
open: no yes
close: no yes
fault: no yes can return with page locked
page_mkwrite: no yes can return with page locked
access: no yes
mmap_sem PageLocked(page)
open: yes
close: yes
fault: yes can return with page locked
page_mkwrite: yes can return with page locked
access: yes
->fault() is called when a previously not present pte is about
to be faulted in. The filesystem must find and return the page associated
@ -539,6 +532,3 @@ VM_IO | VM_PFNMAP VMAs.
(if you break something or notice that it is broken and do not fix it yourself
- at least put it here)
ipc/shm.c::shm_delete() - may need BKL.
->read() and ->write() in many drivers are (probably) missing BKL.