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>

1 files changed, 102 insertions, 112 deletions

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index b6426f15b4a..7686e768449 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -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
-
-        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.
+                        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
+
 --------------------------- 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.