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