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1From 84a03bcb1f1fb5b6a9f6f508fa0a1fae41a5827a Mon Sep 17 00:00:00 2001
2From: Christoph Hellwig <hch>
3Date: Thu, 16 Dec 2010 12:04:54 +0100
4Subject: [PATCH 35/65] update Documentation/filesystems/Locking
5
6Mostly inspired by all the recent BKL removal changes, but a lot of older
7updates also weren't properly recorded.
8
9Signed-off-by: Christoph Hellwig <hch@lst.de>
10Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
11---
12 Documentation/filesystems/Locking | 214 ++++++++++++++++++-------------------
13 1 files changed, 102 insertions(+), 112 deletions(-)
14
15diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
16index b6426f1..7686e76 100644
17--- a/Documentation/filesystems/Locking
18+++ b/Documentation/filesystems/Locking
19@@ -18,7 +18,6 @@ prototypes:
20 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
21
22 locking rules:
23- none have BKL
24 dcache_lock rename_lock ->d_lock may block
25 d_revalidate: no no no yes
26 d_hash no no no yes
27@@ -42,18 +41,23 @@ ata *);
28 int (*rename) (struct inode *, struct dentry *,
29 struct inode *, struct dentry *);
30 int (*readlink) (struct dentry *, char __user *,int);
31- int (*follow_link) (struct dentry *, struct nameidata *);
32+ void * (*follow_link) (struct dentry *, struct nameidata *);
33+ void (*put_link) (struct dentry *, struct nameidata *, void *);
34 void (*truncate) (struct inode *);
35 int (*permission) (struct inode *, int, struct nameidata *);
36+ int (*check_acl)(struct inode *, int);
37 int (*setattr) (struct dentry *, struct iattr *);
38 int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
39 int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
40 ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
41 ssize_t (*listxattr) (struct dentry *, char *, size_t);
42 int (*removexattr) (struct dentry *, const char *);
43+ void (*truncate_range)(struct inode *, loff_t, loff_t);
44+ long (*fallocate)(struct inode *inode, int mode, loff_t offset, loff_t len);
45+ int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
46
47 locking rules:
48- all may block, none have BKL
49+ all may block
50 i_mutex(inode)
51 lookup: yes
52 create: yes
53@@ -66,19 +70,24 @@ rmdir: yes (both) (see below)
54 rename: yes (all) (see below)
55 readlink: no
56 follow_link: no
57+put_link: no
58 truncate: yes (see below)
59 setattr: yes
60 permission: no
61+check_acl: no
62 getattr: no
63 setxattr: yes
64 getxattr: no
65 listxattr: no
66 removexattr: yes
67+truncate_range: yes
68+fallocate: no
69+fiemap: no
70 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
71 victim.
72 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
73 ->truncate() is never called directly - it's a callback, not a
74-method. It's called by vmtruncate() - library function normally used by
75+method. It's called by vmtruncate() - deprecated library function used by
76 ->setattr(). Locking information above applies to that call (i.e. is
77 inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
78 passed).
79@@ -91,7 +100,7 @@ prototypes:
80 struct inode *(*alloc_inode)(struct super_block *sb);
81 void (*destroy_inode)(struct inode *);
82 void (*dirty_inode) (struct inode *);
83- int (*write_inode) (struct inode *, int);
84+ int (*write_inode) (struct inode *, struct writeback_control *wbc);
85 int (*drop_inode) (struct inode *);
86 void (*evict_inode) (struct inode *);
87 void (*put_super) (struct super_block *);
88@@ -105,10 +114,11 @@ prototypes:
89 int (*show_options)(struct seq_file *, struct vfsmount *);
90 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
91 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
92+ int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
93+ int (*trim_fs) (struct super_block *, struct fstrim_range *);
94
95 locking rules:
96 All may block [not true, see below]
97- None have BKL
98 s_umount
99 alloc_inode:
100 destroy_inode:
101@@ -127,6 +137,8 @@ umount_begin: no
102 show_options: no (namespace_sem)
103 quota_read: no (see below)
104 quota_write: no (see below)
105+bdev_try_to_free_page: no (see below)
106+trim_fs: no
107
108 ->statfs() has s_umount (shared) when called by ustat(2) (native or
109 compat), but that's an accident of bad API; s_umount is used to pin
110@@ -139,19 +151,25 @@ be the only ones operating on the quota file by the quota code (via
111 dqio_sem) (unless an admin really wants to screw up something and
112 writes to quota files with quotas on). For other details about locking
113 see also dquot_operations section.
114+->bdev_try_to_free_page is called from the ->releasepage handler of
115+the block device inode. See there for more details.
116
117 --------------------------- file_system_type ---------------------------
118 prototypes:
119 int (*get_sb) (struct file_system_type *, int,
120 const char *, void *, struct vfsmount *);
121+ struct dentry *(*mount) (struct file_system_type *, int,
122+ const char *, void *);
123 void (*kill_sb) (struct super_block *);
124 locking rules:
125- may block BKL
126-get_sb yes no
127-kill_sb yes no
128+ may block
129+get_sb yes
130+mount yes
131+kill_sb yes
132
133 ->get_sb() returns error or 0 with locked superblock attached to the vfsmount
134 (exclusive on ->s_umount).
135+->mount() returns ERR_PTR or the root dentry.
136 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
137 unlocks and drops the reference.
138
139@@ -176,27 +194,35 @@ prototypes:
140 void (*freepage)(struct page *);
141 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
142 loff_t offset, unsigned long nr_segs);
143- int (*launder_page) (struct page *);
144+ int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
145+ unsigned long *);
146+ int (*migratepage)(struct address_space *, struct page *, struct page *);
147+ int (*launder_page)(struct page *);
148+ int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
149+ int (*error_remove_page)(struct address_space *, struct page *);
150
151 locking rules:
152 All except set_page_dirty and freepage may block
153
154- BKL PageLocked(page) i_mutex
155-writepage: no yes, unlocks (see below)
156-readpage: no yes, unlocks
157-sync_page: no maybe
158-writepages: no
159-set_page_dirty no no
160-readpages: no
161-write_begin: no locks the page yes
162-write_end: no yes, unlocks yes
163-perform_write: no n/a yes
164-bmap: no
165-invalidatepage: no yes
166-releasepage: no yes
167-freepage: no yes
168-direct_IO: no
169-launder_page: no yes
170+ PageLocked(page) i_mutex
171+writepage: yes, unlocks (see below)
172+readpage: yes, unlocks
173+sync_page: maybe
174+writepages:
175+set_page_dirty no
176+readpages:
177+write_begin: locks the page yes
178+write_end: yes, unlocks yes
179+bmap:
180+invalidatepage: yes
181+releasepage: yes
182+freepage: yes
183+direct_IO:
184+get_xip_mem: maybe
185+migratepage: yes (both)
186+launder_page: yes
187+is_partially_uptodate: yes
188+error_remove_page: yes
189
190 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
191 may be called from the request handler (/dev/loop).
192@@ -276,9 +302,8 @@ under spinlock (it cannot block) and is sometimes called with the page
193 not locked.
194
195 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
196-filesystems and by the swapper. The latter will eventually go away. All
197-instances do not actually need the BKL. Please, keep it that way and don't
198-breed new callers.
199+filesystems and by the swapper. The latter will eventually go away. Please,
200+keep it that way and don't breed new callers.
201
202 ->invalidatepage() is called when the filesystem must attempt to drop
203 some or all of the buffers from the page when it is being truncated. It
204@@ -299,47 +324,37 @@ cleaned, or an error value if not. Note that in order to prevent the page
205 getting mapped back in and redirtied, it needs to be kept locked
206 across the entire operation.
207
208- Note: currently almost all instances of address_space methods are
209-using BKL for internal serialization and that's one of the worst sources
210-of contention. Normally they are calling library functions (in fs/buffer.c)
211-and pass foo_get_block() as a callback (on local block-based filesystems,
212-indeed). BKL is not needed for library stuff and is usually taken by
213-foo_get_block(). It's an overkill, since block bitmaps can be protected by
214-internal fs locking and real critical areas are much smaller than the areas
215-filesystems protect now.
216-
217 ----------------------- file_lock_operations ------------------------------
218 prototypes:
219- void (*fl_insert)(struct file_lock *); /* lock insertion callback */
220- void (*fl_remove)(struct file_lock *); /* lock removal callback */
221 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
222 void (*fl_release_private)(struct file_lock *);
223
224
225 locking rules:
226- BKL may block
227-fl_insert: yes no
228-fl_remove: yes no
229-fl_copy_lock: yes no
230-fl_release_private: yes yes
231+ file_lock_lock may block
232+fl_copy_lock: yes no
233+fl_release_private: maybe no
234
235 ----------------------- lock_manager_operations ---------------------------
236 prototypes:
237 int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
238 void (*fl_notify)(struct file_lock *); /* unblock callback */
239+ int (*fl_grant)(struct file_lock *, struct file_lock *, int);
240 void (*fl_release_private)(struct file_lock *);
241 void (*fl_break)(struct file_lock *); /* break_lease callback */
242+ int (*fl_mylease)(struct file_lock *, struct file_lock *);
243+ int (*fl_change)(struct file_lock **, int);
244
245 locking rules:
246- BKL may block
247-fl_compare_owner: yes no
248-fl_notify: yes no
249-fl_release_private: yes yes
250-fl_break: yes no
251-
252- Currently only NFSD and NLM provide instances of this class. None of the
253-them block. If you have out-of-tree instances - please, show up. Locking
254-in that area will change.
255+ file_lock_lock may block
256+fl_compare_owner: yes no
257+fl_notify: yes no
258+fl_grant: no no
259+fl_release_private: maybe no
260+fl_break: yes no
261+fl_mylease: yes no
262+fl_change yes no
263+
264 --------------------------- buffer_head -----------------------------------
265 prototypes:
266 void (*b_end_io)(struct buffer_head *bh, int uptodate);
267@@ -364,17 +379,17 @@ prototypes:
268 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
269
270 locking rules:
271- BKL bd_mutex
272-open: no yes
273-release: no yes
274-ioctl: no no
275-compat_ioctl: no no
276-direct_access: no no
277-media_changed: no no
278-unlock_native_capacity: no no
279-revalidate_disk: no no
280-getgeo: no no
281-swap_slot_free_notify: no no (see below)
282+ bd_mutex
283+open: yes
284+release: yes
285+ioctl: no
286+compat_ioctl: no
287+direct_access: no
288+media_changed: no
289+unlock_native_capacity: no
290+revalidate_disk: no
291+getgeo: no
292+swap_slot_free_notify: no (see below)
293
294 media_changed, unlock_native_capacity and revalidate_disk are called only from
295 check_disk_change().
296@@ -413,34 +428,21 @@ prototypes:
297 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
298 unsigned long, unsigned long, unsigned long);
299 int (*check_flags)(int);
300+ int (*flock) (struct file *, int, struct file_lock *);
301+ ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
302+ size_t, unsigned int);
303+ ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
304+ size_t, unsigned int);
305+ int (*setlease)(struct file *, long, struct file_lock **);
306 };
307
308 locking rules:
309- All may block.
310- BKL
311-llseek: no (see below)
312-read: no
313-aio_read: no
314-write: no
315-aio_write: no
316-readdir: no
317-poll: no
318-unlocked_ioctl: no
319-compat_ioctl: no
320-mmap: no
321-open: no
322-flush: no
323-release: no
324-fsync: no (see below)
325-aio_fsync: no
326-fasync: no
327-lock: yes
328-readv: no
329-writev: no
330-sendfile: no
331-sendpage: no
332-get_unmapped_area: no
333-check_flags: no
334+ All may block except for ->setlease.
335+ No VFS locks held on entry except for ->fsync and ->setlease.
336+
337+->fsync() has i_mutex on inode.
338+
339+->setlease has the file_list_lock held and must not sleep.
340
341 ->llseek() locking has moved from llseek to the individual llseek
342 implementations. If your fs is not using generic_file_llseek, you
343@@ -450,17 +452,10 @@ mutex or just to use i_size_read() instead.
344 Note: this does not protect the file->f_pos against concurrent modifications
345 since this is something the userspace has to take care about.
346
347-Note: ext2_release() was *the* source of contention on fs-intensive
348-loads and dropping BKL on ->release() helps to get rid of that (we still
349-grab BKL for cases when we close a file that had been opened r/w, but that
350-can and should be done using the internal locking with smaller critical areas).
351-Current worst offender is ext2_get_block()...
352-
353-->fasync() is called without BKL protection, and is responsible for
354-maintaining the FASYNC bit in filp->f_flags. Most instances call
355-fasync_helper(), which does that maintenance, so it's not normally
356-something one needs to worry about. Return values > 0 will be mapped to
357-zero in the VFS layer.
358+->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
359+Most instances call fasync_helper(), which does that maintenance, so it's
360+not normally something one needs to worry about. Return values > 0 will be
361+mapped to zero in the VFS layer.
362
363 ->readdir() and ->ioctl() on directories must be changed. Ideally we would
364 move ->readdir() to inode_operations and use a separate method for directory
365@@ -471,8 +466,6 @@ components. And there are other reasons why the current interface is a mess...
366 ->read on directories probably must go away - we should just enforce -EISDIR
367 in sys_read() and friends.
368
369-->fsync() has i_mutex on inode.
370-
371 --------------------------- dquot_operations -------------------------------
372 prototypes:
373 int (*write_dquot) (struct dquot *);
374@@ -507,12 +500,12 @@ prototypes:
375 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
376
377 locking rules:
378- BKL mmap_sem PageLocked(page)
379-open: no yes
380-close: no yes
381-fault: no yes can return with page locked
382-page_mkwrite: no yes can return with page locked
383-access: no yes
384+ mmap_sem PageLocked(page)
385+open: yes
386+close: yes
387+fault: yes can return with page locked
388+page_mkwrite: yes can return with page locked
389+access: yes
390
391 ->fault() is called when a previously not present pte is about
392 to be faulted in. The filesystem must find and return the page associated
393@@ -539,6 +532,3 @@ VM_IO | VM_PFNMAP VMAs.
394
395 (if you break something or notice that it is broken and do not fix it yourself
396 - at least put it here)
397-
398-ipc/shm.c::shm_delete() - may need BKL.
399-->read() and ->write() in many drivers are (probably) missing BKL.
400--
4011.6.6.1
402
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