| blob | 5b0c083d7c0e98eccfb315cf6b5cd72f8e73d7e5 |
1 The text below describes the locking rules for VFS-related methods.
2 It is (believed to be) up-to-date. *Please*, if you change anything in
3 prototypes or locking protocols - update this file. And update the relevant
4 instances in the tree, don't leave that to maintainers of filesystems/devices/
5 etc. At the very least, put the list of dubious cases in the end of this file.
6 Don't turn it into log - maintainers of out-of-the-tree code are supposed to
7 be able to use diff(1).
8 Thing currently missing here: socket operations. Alexey?
10 --------------------------- dentry_operations --------------------------
11 prototypes:
12 int (*d_revalidate)(struct dentry *, unsigned int);
13 int (*d_weak_revalidate)(struct dentry *, unsigned int);
14 int (*d_hash)(const struct dentry *, struct qstr *);
15 int (*d_compare)(const struct dentry *, const struct dentry *,
16 unsigned int, const char *, const struct qstr *);
17 int (*d_delete)(struct dentry *);
18 void (*d_release)(struct dentry *);
19 void (*d_iput)(struct dentry *, struct inode *);
20 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
21 struct vfsmount *(*d_automount)(struct path *path);
22 int (*d_manage)(struct dentry *, bool);
24 locking rules:
25 rename_lock ->d_lock may block rcu-walk
26 d_revalidate: no no yes (ref-walk) maybe
27 d_weak_revalidate:no no yes no
28 d_hash no no no maybe
29 d_compare: yes no no maybe
30 d_delete: no yes no no
31 d_release: no no yes no
32 d_prune: no yes no no
33 d_iput: no no yes no
34 d_dname: no no no no
35 d_automount: no no yes no
36 d_manage: no no yes (ref-walk) maybe
38 --------------------------- inode_operations ---------------------------
39 prototypes:
40 int (*create) (struct inode *,struct dentry *,umode_t, bool);
41 struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
42 int (*link) (struct dentry *,struct inode *,struct dentry *);
43 int (*unlink) (struct inode *,struct dentry *);
44 int (*symlink) (struct inode *,struct dentry *,const char *);
45 int (*mkdir) (struct inode *,struct dentry *,umode_t);
46 int (*rmdir) (struct inode *,struct dentry *);
47 int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
48 int (*rename) (struct inode *, struct dentry *,
49 struct inode *, struct dentry *);
50 int (*readlink) (struct dentry *, char __user *,int);
51 void * (*follow_link) (struct dentry *, struct nameidata *);
52 void (*put_link) (struct dentry *, struct nameidata *, void *);
53 void (*truncate) (struct inode *);
54 int (*permission) (struct inode *, int, unsigned int);
55 int (*get_acl)(struct inode *, int);
56 int (*setattr) (struct dentry *, struct iattr *);
57 int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
58 int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
59 ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
60 ssize_t (*listxattr) (struct dentry *, char *, size_t);
61 int (*removexattr) (struct dentry *, const char *);
62 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
63 void (*update_time)(struct inode *, struct timespec *, int);
64 int (*atomic_open)(struct inode *, struct dentry *,
65 struct file *, unsigned open_flag,
66 umode_t create_mode, int *opened);
67 int (*tmpfile) (struct inode *, struct dentry *, umode_t);
69 locking rules:
70 all may block
71 i_mutex(inode)
72 lookup: yes
73 create: yes
74 link: yes (both)
75 mknod: yes
76 symlink: yes
77 mkdir: yes
78 unlink: yes (both)
79 rmdir: yes (both) (see below)
80 rename: yes (all) (see below)
81 readlink: no
82 follow_link: no
83 put_link: no
84 setattr: yes
85 permission: no (may not block if called in rcu-walk mode)
86 get_acl: no
87 getattr: no
88 setxattr: yes
89 getxattr: no
90 listxattr: no
91 removexattr: yes
92 fiemap: no
93 update_time: no
94 atomic_open: yes
95 tmpfile: no
97 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
98 victim.
99 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
101 See Documentation/filesystems/directory-locking for more detailed discussion
102 of the locking scheme for directory operations.
104 --------------------------- super_operations ---------------------------
105 prototypes:
106 struct inode *(*alloc_inode)(struct super_block *sb);
107 void (*destroy_inode)(struct inode *);
108 void (*dirty_inode) (struct inode *, int flags);
109 int (*write_inode) (struct inode *, struct writeback_control *wbc);
110 int (*drop_inode) (struct inode *);
111 void (*evict_inode) (struct inode *);
112 void (*put_super) (struct super_block *);
113 int (*sync_fs)(struct super_block *sb, int wait);
114 int (*freeze_fs) (struct super_block *);
115 int (*unfreeze_fs) (struct super_block *);
116 int (*statfs) (struct dentry *, struct kstatfs *);
117 int (*remount_fs) (struct super_block *, int *, char *);
118 void (*umount_begin) (struct super_block *);
119 int (*show_options)(struct seq_file *, struct dentry *);
120 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
121 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
122 int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
124 locking rules:
125 All may block [not true, see below]
126 s_umount
127 alloc_inode:
128 destroy_inode:
129 dirty_inode:
130 write_inode:
131 drop_inode: !!!inode->i_lock!!!
132 evict_inode:
133 put_super: write
134 sync_fs: read
135 freeze_fs: write
136 unfreeze_fs: write
137 statfs: maybe(read) (see below)
138 remount_fs: write
139 umount_begin: no
140 show_options: no (namespace_sem)
141 quota_read: no (see below)
142 quota_write: no (see below)
143 bdev_try_to_free_page: no (see below)
145 ->statfs() has s_umount (shared) when called by ustat(2) (native or
146 compat), but that's an accident of bad API; s_umount is used to pin
147 the superblock down when we only have dev_t given us by userland to
148 identify the superblock. Everything else (statfs(), fstatfs(), etc.)
149 doesn't hold it when calling ->statfs() - superblock is pinned down
150 by resolving the pathname passed to syscall.
151 ->quota_read() and ->quota_write() functions are both guaranteed to
152 be the only ones operating on the quota file by the quota code (via
153 dqio_sem) (unless an admin really wants to screw up something and
154 writes to quota files with quotas on). For other details about locking
155 see also dquot_operations section.
156 ->bdev_try_to_free_page is called from the ->releasepage handler of
157 the block device inode. See there for more details.
159 --------------------------- file_system_type ---------------------------
160 prototypes:
161 int (*get_sb) (struct file_system_type *, int,
162 const char *, void *, struct vfsmount *);
163 struct dentry *(*mount) (struct file_system_type *, int,
164 const char *, void *);
165 void (*kill_sb) (struct super_block *);
166 locking rules:
167 may block
168 mount yes
169 kill_sb yes
171 ->mount() returns ERR_PTR or the root dentry; its superblock should be locked
172 on return.
173 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
174 unlocks and drops the reference.
176 --------------------------- address_space_operations --------------------------
177 prototypes:
178 int (*writepage)(struct page *page, struct writeback_control *wbc);
179 int (*readpage)(struct file *, struct page *);
180 int (*sync_page)(struct page *);
181 int (*writepages)(struct address_space *, struct writeback_control *);
182 int (*set_page_dirty)(struct page *page);
183 int (*readpages)(struct file *filp, struct address_space *mapping,
184 struct list_head *pages, unsigned nr_pages);
185 int (*write_begin)(struct file *, struct address_space *mapping,
186 loff_t pos, unsigned len, unsigned flags,
187 struct page **pagep, void **fsdata);
188 int (*write_end)(struct file *, struct address_space *mapping,
189 loff_t pos, unsigned len, unsigned copied,
190 struct page *page, void *fsdata);
191 sector_t (*bmap)(struct address_space *, sector_t);
192 void (*invalidatepage) (struct page *, unsigned int, unsigned int);
193 int (*releasepage) (struct page *, int);
194 void (*freepage)(struct page *);
195 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
196 loff_t offset, unsigned long nr_segs);
197 int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
198 unsigned long *);
199 int (*migratepage)(struct address_space *, struct page *, struct page *);
200 int (*launder_page)(struct page *);
201 int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
202 int (*error_remove_page)(struct address_space *, struct page *);
203 int (*swap_activate)(struct file *);
204 int (*swap_deactivate)(struct file *);
206 locking rules:
207 All except set_page_dirty and freepage may block
209 PageLocked(page) i_mutex
210 writepage: yes, unlocks (see below)
211 readpage: yes, unlocks
212 sync_page: maybe
213 writepages:
214 set_page_dirty no
215 readpages:
216 write_begin: locks the page yes
217 write_end: yes, unlocks yes
218 bmap:
219 invalidatepage: yes
220 releasepage: yes
221 freepage: yes
222 direct_IO:
223 get_xip_mem: maybe
224 migratepage: yes (both)
225 launder_page: yes
226 is_partially_uptodate: yes
227 error_remove_page: yes
228 swap_activate: no
229 swap_deactivate: no
231 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
232 may be called from the request handler (/dev/loop).
234 ->readpage() unlocks the page, either synchronously or via I/O
235 completion.
237 ->readpages() populates the pagecache with the passed pages and starts
238 I/O against them. They come unlocked upon I/O completion.
240 ->writepage() is used for two purposes: for "memory cleansing" and for
241 "sync". These are quite different operations and the behaviour may differ
242 depending upon the mode.
244 If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
245 it *must* start I/O against the page, even if that would involve
246 blocking on in-progress I/O.
248 If writepage is called for memory cleansing (sync_mode ==
249 WBC_SYNC_NONE) then its role is to get as much writeout underway as
250 possible. So writepage should try to avoid blocking against
251 currently-in-progress I/O.
253 If the filesystem is not called for "sync" and it determines that it
254 would need to block against in-progress I/O to be able to start new I/O
255 against the page the filesystem should redirty the page with
256 redirty_page_for_writepage(), then unlock the page and return zero.
257 This may also be done to avoid internal deadlocks, but rarely.
259 If the filesystem is called for sync then it must wait on any
260 in-progress I/O and then start new I/O.
262 The filesystem should unlock the page synchronously, before returning to the
263 caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
264 value. WRITEPAGE_ACTIVATE means that page cannot really be written out
265 currently, and VM should stop calling ->writepage() on this page for some
266 time. VM does this by moving page to the head of the active list, hence the
267 name.
269 Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
270 and return zero, writepage *must* run set_page_writeback() against the page,
271 followed by unlocking it. Once set_page_writeback() has been run against the
272 page, write I/O can be submitted and the write I/O completion handler must run
273 end_page_writeback() once the I/O is complete. If no I/O is submitted, the
274 filesystem must run end_page_writeback() against the page before returning from
275 writepage.
277 That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
278 if the filesystem needs the page to be locked during writeout, that is ok, too,
279 the page is allowed to be unlocked at any point in time between the calls to
280 set_page_writeback() and end_page_writeback().
282 Note, failure to run either redirty_page_for_writepage() or the combination of
283 set_page_writeback()/end_page_writeback() on a page submitted to writepage
284 will leave the page itself marked clean but it will be tagged as dirty in the
285 radix tree. This incoherency can lead to all sorts of hard-to-debug problems
286 in the filesystem like having dirty inodes at umount and losing written data.
288 ->sync_page() locking rules are not well-defined - usually it is called
289 with lock on page, but that is not guaranteed. Considering the currently
290 existing instances of this method ->sync_page() itself doesn't look
291 well-defined...
293 ->writepages() is used for periodic writeback and for syscall-initiated
294 sync operations. The address_space should start I/O against at least
295 *nr_to_write pages. *nr_to_write must be decremented for each page which is
296 written. The address_space implementation may write more (or less) pages
297 than *nr_to_write asks for, but it should try to be reasonably close. If
298 nr_to_write is NULL, all dirty pages must be written.
300 writepages should _only_ write pages which are present on
301 mapping->io_pages.
303 ->set_page_dirty() is called from various places in the kernel
304 when the target page is marked as needing writeback. It may be called
305 under spinlock (it cannot block) and is sometimes called with the page
306 not locked.
308 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
309 filesystems and by the swapper. The latter will eventually go away. Please,
310 keep it that way and don't breed new callers.
312 ->invalidatepage() is called when the filesystem must attempt to drop
313 some or all of the buffers from the page when it is being truncated. It
314 returns zero on success. If ->invalidatepage is zero, the kernel uses
315 block_invalidatepage() instead.
317 ->releasepage() is called when the kernel is about to try to drop the
318 buffers from the page in preparation for freeing it. It returns zero to
319 indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
320 the kernel assumes that the fs has no private interest in the buffers.
322 ->freepage() is called when the kernel is done dropping the page
323 from the page cache.
325 ->launder_page() may be called prior to releasing a page if
326 it is still found to be dirty. It returns zero if the page was successfully
327 cleaned, or an error value if not. Note that in order to prevent the page
328 getting mapped back in and redirtied, it needs to be kept locked
329 across the entire operation.
331 ->swap_activate will be called with a non-zero argument on
332 files backing (non block device backed) swapfiles. A return value
333 of zero indicates success, in which case this file can be used for
334 backing swapspace. The swapspace operations will be proxied to the
335 address space operations.
337 ->swap_deactivate() will be called in the sys_swapoff()
338 path after ->swap_activate() returned success.
340 ----------------------- file_lock_operations ------------------------------
341 prototypes:
342 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
343 void (*fl_release_private)(struct file_lock *);
346 locking rules:
347 inode->i_lock may block
348 fl_copy_lock: yes no
349 fl_release_private: maybe no
351 ----------------------- lock_manager_operations ---------------------------
352 prototypes:
353 int (*lm_compare_owner)(struct file_lock *, struct file_lock *);
354 unsigned long (*lm_owner_key)(struct file_lock *);
355 void (*lm_notify)(struct file_lock *); /* unblock callback */
356 int (*lm_grant)(struct file_lock *, struct file_lock *, int);
357 void (*lm_break)(struct file_lock *); /* break_lease callback */
358 int (*lm_change)(struct file_lock **, int);
360 locking rules:
362 inode->i_lock blocked_lock_lock may block
363 lm_compare_owner: yes[1] maybe no
364 lm_owner_key yes[1] yes no
365 lm_notify: yes yes no
366 lm_grant: no no no
367 lm_break: yes no no
368 lm_change yes no no
370 [1]: ->lm_compare_owner and ->lm_owner_key are generally called with
371 *an* inode->i_lock held. It may not be the i_lock of the inode
372 associated with either file_lock argument! This is the case with deadlock
373 detection, since the code has to chase down the owners of locks that may
374 be entirely unrelated to the one on which the lock is being acquired.
375 For deadlock detection however, the blocked_lock_lock is also held. The
376 fact that these locks are held ensures that the file_locks do not
377 disappear out from under you while doing the comparison or generating an
378 owner key.
380 --------------------------- buffer_head -----------------------------------
381 prototypes:
382 void (*b_end_io)(struct buffer_head *bh, int uptodate);
384 locking rules:
385 called from interrupts. In other words, extreme care is needed here.
386 bh is locked, but that's all warranties we have here. Currently only RAID1,
387 highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
388 call this method upon the IO completion.
390 --------------------------- block_device_operations -----------------------
391 prototypes:
392 int (*open) (struct block_device *, fmode_t);
393 int (*release) (struct gendisk *, fmode_t);
394 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
395 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
396 int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
397 int (*media_changed) (struct gendisk *);
398 void (*unlock_native_capacity) (struct gendisk *);
399 int (*revalidate_disk) (struct gendisk *);
400 int (*getgeo)(struct block_device *, struct hd_geometry *);
401 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
403 locking rules:
404 bd_mutex
405 open: yes
406 release: yes
407 ioctl: no
408 compat_ioctl: no
409 direct_access: no
410 media_changed: no
411 unlock_native_capacity: no
412 revalidate_disk: no
413 getgeo: no
414 swap_slot_free_notify: no (see below)
416 media_changed, unlock_native_capacity and revalidate_disk are called only from
417 check_disk_change().
419 swap_slot_free_notify is called with swap_lock and sometimes the page lock
420 held.
423 --------------------------- file_operations -------------------------------
424 prototypes:
425 loff_t (*llseek) (struct file *, loff_t, int);
426 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
427 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
428 ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
429 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
430 int (*iterate) (struct file *, struct dir_context *);
431 unsigned int (*poll) (struct file *, struct poll_table_struct *);
432 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
433 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
434 int (*mmap) (struct file *, struct vm_area_struct *);
435 int (*open) (struct inode *, struct file *);
436 int (*flush) (struct file *);
437 int (*release) (struct inode *, struct file *);
438 int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
439 int (*aio_fsync) (struct kiocb *, int datasync);
440 int (*fasync) (int, struct file *, int);
441 int (*lock) (struct file *, int, struct file_lock *);
442 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
443 loff_t *);
444 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
445 loff_t *);
446 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
447 void __user *);
448 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
449 loff_t *, int);
450 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
451 unsigned long, unsigned long, unsigned long);
452 int (*check_flags)(int);
453 int (*flock) (struct file *, int, struct file_lock *);
454 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
455 size_t, unsigned int);
456 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
457 size_t, unsigned int);
458 int (*setlease)(struct file *, long, struct file_lock **);
459 long (*fallocate)(struct file *, int, loff_t, loff_t);
460 };
462 locking rules:
463 All may block except for ->setlease.
464 No VFS locks held on entry except for ->setlease.
466 ->setlease has the file_list_lock held and must not sleep.
468 ->llseek() locking has moved from llseek to the individual llseek
469 implementations. If your fs is not using generic_file_llseek, you
470 need to acquire and release the appropriate locks in your ->llseek().
471 For many filesystems, it is probably safe to acquire the inode
472 mutex or just to use i_size_read() instead.
473 Note: this does not protect the file->f_pos against concurrent modifications
474 since this is something the userspace has to take care about.
476 ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
477 Most instances call fasync_helper(), which does that maintenance, so it's
478 not normally something one needs to worry about. Return values > 0 will be
479 mapped to zero in the VFS layer.
481 ->readdir() and ->ioctl() on directories must be changed. Ideally we would
482 move ->readdir() to inode_operations and use a separate method for directory
483 ->ioctl() or kill the latter completely. One of the problems is that for
484 anything that resembles union-mount we won't have a struct file for all
485 components. And there are other reasons why the current interface is a mess...
487 ->read on directories probably must go away - we should just enforce -EISDIR
488 in sys_read() and friends.
490 --------------------------- dquot_operations -------------------------------
491 prototypes:
492 int (*write_dquot) (struct dquot *);
493 int (*acquire_dquot) (struct dquot *);
494 int (*release_dquot) (struct dquot *);
495 int (*mark_dirty) (struct dquot *);
496 int (*write_info) (struct super_block *, int);
498 These operations are intended to be more or less wrapping functions that ensure
499 a proper locking wrt the filesystem and call the generic quota operations.
501 What filesystem should expect from the generic quota functions:
503 FS recursion Held locks when called
504 write_dquot: yes dqonoff_sem or dqptr_sem
505 acquire_dquot: yes dqonoff_sem or dqptr_sem
506 release_dquot: yes dqonoff_sem or dqptr_sem
507 mark_dirty: no -
508 write_info: yes dqonoff_sem
510 FS recursion means calling ->quota_read() and ->quota_write() from superblock
511 operations.
513 More details about quota locking can be found in fs/dquot.c.
515 --------------------------- vm_operations_struct -----------------------------
516 prototypes:
517 void (*open)(struct vm_area_struct*);
518 void (*close)(struct vm_area_struct*);
519 int (*fault)(struct vm_area_struct*, struct vm_fault *);
520 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
521 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
523 locking rules:
524 mmap_sem PageLocked(page)
525 open: yes
526 close: yes
527 fault: yes can return with page locked
528 page_mkwrite: yes can return with page locked
529 access: yes
531 ->fault() is called when a previously not present pte is about
532 to be faulted in. The filesystem must find and return the page associated
533 with the passed in "pgoff" in the vm_fault structure. If it is possible that
534 the page may be truncated and/or invalidated, then the filesystem must lock
535 the page, then ensure it is not already truncated (the page lock will block
536 subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
537 locked. The VM will unlock the page.
539 ->page_mkwrite() is called when a previously read-only pte is
540 about to become writeable. The filesystem again must ensure that there are
541 no truncate/invalidate races, and then return with the page locked. If
542 the page has been truncated, the filesystem should not look up a new page
543 like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
544 will cause the VM to retry the fault.
546 ->access() is called when get_user_pages() fails in
547 access_process_vm(), typically used to debug a process through
548 /proc/pid/mem or ptrace. This function is needed only for
549 VM_IO | VM_PFNMAP VMAs.
551 ================================================================================
552 Dubious stuff
554 (if you break something or notice that it is broken and do not fix it yourself
555 - at least put it here)