| blob | 61b31acb9176b35bc77c914b2b3913abbcc9e78a |
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 *, struct nameidata *);
13 int (*d_hash)(const struct dentry *, const struct inode *,
14 struct qstr *);
15 int (*d_compare)(const struct dentry *, const struct inode *,
16 const struct dentry *, const struct inode *,
17 unsigned int, const char *, const struct qstr *);
18 int (*d_delete)(struct dentry *);
19 void (*d_release)(struct dentry *);
20 void (*d_iput)(struct dentry *, struct inode *);
21 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
22 struct vfsmount *(*d_automount)(struct path *path);
23 int (*d_manage)(struct dentry *, bool);
25 locking rules:
26 rename_lock ->d_lock may block rcu-walk
27 d_revalidate: no no yes (ref-walk) maybe
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_iput: no no yes no
33 d_dname: no no no no
34 d_automount: no no yes no
35 d_manage: no no yes (ref-walk) maybe
37 --------------------------- inode_operations ---------------------------
38 prototypes:
39 int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
40 struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
41 ata *);
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 *,int);
46 int (*rmdir) (struct inode *,struct dentry *);
47 int (*mknod) (struct inode *,struct dentry *,int,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 (*check_acl)(struct inode *, int, unsigned 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 void (*truncate_range)(struct inode *, loff_t, loff_t);
63 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
65 locking rules:
66 all may block
67 i_mutex(inode)
68 lookup: yes
69 create: yes
70 link: yes (both)
71 mknod: yes
72 symlink: yes
73 mkdir: yes
74 unlink: yes (both)
75 rmdir: yes (both) (see below)
76 rename: yes (all) (see below)
77 readlink: no
78 follow_link: no
79 put_link: no
80 truncate: yes (see below)
81 setattr: yes
82 permission: no (may not block if called in rcu-walk mode)
83 check_acl: no
84 getattr: no
85 setxattr: yes
86 getxattr: no
87 listxattr: no
88 removexattr: yes
89 truncate_range: yes
90 fiemap: no
91 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
92 victim.
93 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
94 ->truncate() is never called directly - it's a callback, not a
95 method. It's called by vmtruncate() - deprecated library function used by
96 ->setattr(). Locking information above applies to that call (i.e. is
97 inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
98 passed).
100 See Documentation/filesystems/directory-locking for more detailed discussion
101 of the locking scheme for directory operations.
103 --------------------------- super_operations ---------------------------
104 prototypes:
105 struct inode *(*alloc_inode)(struct super_block *sb);
106 void (*destroy_inode)(struct inode *);
107 void (*dirty_inode) (struct inode *);
108 int (*write_inode) (struct inode *, struct writeback_control *wbc);
109 int (*drop_inode) (struct inode *);
110 void (*evict_inode) (struct inode *);
111 void (*put_super) (struct super_block *);
112 void (*write_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 vfsmount *);
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: (must not sleep)
130 write_inode:
131 drop_inode: !!!inode->i_lock!!!
132 evict_inode:
133 put_super: write
134 write_super: read
135 sync_fs: read
136 freeze_fs: read
137 unfreeze_fs: read
138 statfs: maybe(read) (see below)
139 remount_fs: write
140 umount_begin: no
141 show_options: no (namespace_sem)
142 quota_read: no (see below)
143 quota_write: no (see below)
144 bdev_try_to_free_page: no (see below)
146 ->statfs() has s_umount (shared) when called by ustat(2) (native or
147 compat), but that's an accident of bad API; s_umount is used to pin
148 the superblock down when we only have dev_t given us by userland to
149 identify the superblock. Everything else (statfs(), fstatfs(), etc.)
150 doesn't hold it when calling ->statfs() - superblock is pinned down
151 by resolving the pathname passed to syscall.
152 ->quota_read() and ->quota_write() functions are both guaranteed to
153 be the only ones operating on the quota file by the quota code (via
154 dqio_sem) (unless an admin really wants to screw up something and
155 writes to quota files with quotas on). For other details about locking
156 see also dquot_operations section.
157 ->bdev_try_to_free_page is called from the ->releasepage handler of
158 the block device inode. See there for more details.
160 --------------------------- file_system_type ---------------------------
161 prototypes:
162 int (*get_sb) (struct file_system_type *, int,
163 const char *, void *, struct vfsmount *);
164 struct dentry *(*mount) (struct file_system_type *, int,
165 const char *, void *);
166 void (*kill_sb) (struct super_block *);
167 locking rules:
168 may block
169 mount yes
170 kill_sb yes
172 ->mount() returns ERR_PTR or the root dentry; its superblock should be locked
173 on return.
174 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
175 unlocks and drops the reference.
177 --------------------------- address_space_operations --------------------------
178 prototypes:
179 int (*writepage)(struct page *page, struct writeback_control *wbc);
180 int (*readpage)(struct file *, struct page *);
181 int (*sync_page)(struct page *);
182 int (*writepages)(struct address_space *, struct writeback_control *);
183 int (*set_page_dirty)(struct page *page);
184 int (*readpages)(struct file *filp, struct address_space *mapping,
185 struct list_head *pages, unsigned nr_pages);
186 int (*write_begin)(struct file *, struct address_space *mapping,
187 loff_t pos, unsigned len, unsigned flags,
188 struct page **pagep, void **fsdata);
189 int (*write_end)(struct file *, struct address_space *mapping,
190 loff_t pos, unsigned len, unsigned copied,
191 struct page *page, void *fsdata);
192 sector_t (*bmap)(struct address_space *, sector_t);
193 int (*invalidatepage) (struct page *, unsigned long);
194 int (*releasepage) (struct page *, int);
195 void (*freepage)(struct page *);
196 int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
197 loff_t offset, unsigned long nr_segs);
198 int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
199 unsigned long *);
200 int (*migratepage)(struct address_space *, struct page *, struct page *);
201 int (*launder_page)(struct page *);
202 int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
203 int (*error_remove_page)(struct address_space *, struct page *);
205 locking rules:
206 All except set_page_dirty and freepage may block
208 PageLocked(page) i_mutex
209 writepage: yes, unlocks (see below)
210 readpage: yes, unlocks
211 sync_page: maybe
212 writepages:
213 set_page_dirty no
214 readpages:
215 write_begin: locks the page yes
216 write_end: yes, unlocks yes
217 bmap:
218 invalidatepage: yes
219 releasepage: yes
220 freepage: yes
221 direct_IO:
222 get_xip_mem: maybe
223 migratepage: yes (both)
224 launder_page: yes
225 is_partially_uptodate: yes
226 error_remove_page: yes
228 ->write_begin(), ->write_end(), ->sync_page() and ->readpage()
229 may be called from the request handler (/dev/loop).
231 ->readpage() unlocks the page, either synchronously or via I/O
232 completion.
234 ->readpages() populates the pagecache with the passed pages and starts
235 I/O against them. They come unlocked upon I/O completion.
237 ->writepage() is used for two purposes: for "memory cleansing" and for
238 "sync". These are quite different operations and the behaviour may differ
239 depending upon the mode.
241 If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
242 it *must* start I/O against the page, even if that would involve
243 blocking on in-progress I/O.
245 If writepage is called for memory cleansing (sync_mode ==
246 WBC_SYNC_NONE) then its role is to get as much writeout underway as
247 possible. So writepage should try to avoid blocking against
248 currently-in-progress I/O.
250 If the filesystem is not called for "sync" and it determines that it
251 would need to block against in-progress I/O to be able to start new I/O
252 against the page the filesystem should redirty the page with
253 redirty_page_for_writepage(), then unlock the page and return zero.
254 This may also be done to avoid internal deadlocks, but rarely.
256 If the filesystem is called for sync then it must wait on any
257 in-progress I/O and then start new I/O.
259 The filesystem should unlock the page synchronously, before returning to the
260 caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
261 value. WRITEPAGE_ACTIVATE means that page cannot really be written out
262 currently, and VM should stop calling ->writepage() on this page for some
263 time. VM does this by moving page to the head of the active list, hence the
264 name.
266 Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
267 and return zero, writepage *must* run set_page_writeback() against the page,
268 followed by unlocking it. Once set_page_writeback() has been run against the
269 page, write I/O can be submitted and the write I/O completion handler must run
270 end_page_writeback() once the I/O is complete. If no I/O is submitted, the
271 filesystem must run end_page_writeback() against the page before returning from
272 writepage.
274 That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
275 if the filesystem needs the page to be locked during writeout, that is ok, too,
276 the page is allowed to be unlocked at any point in time between the calls to
277 set_page_writeback() and end_page_writeback().
279 Note, failure to run either redirty_page_for_writepage() or the combination of
280 set_page_writeback()/end_page_writeback() on a page submitted to writepage
281 will leave the page itself marked clean but it will be tagged as dirty in the
282 radix tree. This incoherency can lead to all sorts of hard-to-debug problems
283 in the filesystem like having dirty inodes at umount and losing written data.
285 ->sync_page() locking rules are not well-defined - usually it is called
286 with lock on page, but that is not guaranteed. Considering the currently
287 existing instances of this method ->sync_page() itself doesn't look
288 well-defined...
290 ->writepages() is used for periodic writeback and for syscall-initiated
291 sync operations. The address_space should start I/O against at least
292 *nr_to_write pages. *nr_to_write must be decremented for each page which is
293 written. The address_space implementation may write more (or less) pages
294 than *nr_to_write asks for, but it should try to be reasonably close. If
295 nr_to_write is NULL, all dirty pages must be written.
297 writepages should _only_ write pages which are present on
298 mapping->io_pages.
300 ->set_page_dirty() is called from various places in the kernel
301 when the target page is marked as needing writeback. It may be called
302 under spinlock (it cannot block) and is sometimes called with the page
303 not locked.
305 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
306 filesystems and by the swapper. The latter will eventually go away. Please,
307 keep it that way and don't breed new callers.
309 ->invalidatepage() is called when the filesystem must attempt to drop
310 some or all of the buffers from the page when it is being truncated. It
311 returns zero on success. If ->invalidatepage is zero, the kernel uses
312 block_invalidatepage() instead.
314 ->releasepage() is called when the kernel is about to try to drop the
315 buffers from the page in preparation for freeing it. It returns zero to
316 indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
317 the kernel assumes that the fs has no private interest in the buffers.
319 ->freepage() is called when the kernel is done dropping the page
320 from the page cache.
322 ->launder_page() may be called prior to releasing a page if
323 it is still found to be dirty. It returns zero if the page was successfully
324 cleaned, or an error value if not. Note that in order to prevent the page
325 getting mapped back in and redirtied, it needs to be kept locked
326 across the entire operation.
328 ----------------------- file_lock_operations ------------------------------
329 prototypes:
330 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
331 void (*fl_release_private)(struct file_lock *);
334 locking rules:
335 file_lock_lock may block
336 fl_copy_lock: yes no
337 fl_release_private: maybe no
339 ----------------------- lock_manager_operations ---------------------------
340 prototypes:
341 int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
342 void (*fl_notify)(struct file_lock *); /* unblock callback */
343 int (*fl_grant)(struct file_lock *, struct file_lock *, int);
344 void (*fl_release_private)(struct file_lock *);
345 void (*fl_break)(struct file_lock *); /* break_lease callback */
346 int (*fl_change)(struct file_lock **, int);
348 locking rules:
349 file_lock_lock may block
350 fl_compare_owner: yes no
351 fl_notify: yes no
352 fl_grant: no no
353 fl_release_private: maybe no
354 fl_break: yes no
355 fl_change yes no
357 --------------------------- buffer_head -----------------------------------
358 prototypes:
359 void (*b_end_io)(struct buffer_head *bh, int uptodate);
361 locking rules:
362 called from interrupts. In other words, extreme care is needed here.
363 bh is locked, but that's all warranties we have here. Currently only RAID1,
364 highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
365 call this method upon the IO completion.
367 --------------------------- block_device_operations -----------------------
368 prototypes:
369 int (*open) (struct block_device *, fmode_t);
370 int (*release) (struct gendisk *, fmode_t);
371 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
372 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
373 int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
374 int (*media_changed) (struct gendisk *);
375 void (*unlock_native_capacity) (struct gendisk *);
376 int (*revalidate_disk) (struct gendisk *);
377 int (*getgeo)(struct block_device *, struct hd_geometry *);
378 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
380 locking rules:
381 bd_mutex
382 open: yes
383 release: yes
384 ioctl: no
385 compat_ioctl: no
386 direct_access: no
387 media_changed: no
388 unlock_native_capacity: no
389 revalidate_disk: no
390 getgeo: no
391 swap_slot_free_notify: no (see below)
393 media_changed, unlock_native_capacity and revalidate_disk are called only from
394 check_disk_change().
396 swap_slot_free_notify is called with swap_lock and sometimes the page lock
397 held.
400 --------------------------- file_operations -------------------------------
401 prototypes:
402 loff_t (*llseek) (struct file *, loff_t, int);
403 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
404 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
405 ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
406 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
407 int (*readdir) (struct file *, void *, filldir_t);
408 unsigned int (*poll) (struct file *, struct poll_table_struct *);
409 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
410 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
411 int (*mmap) (struct file *, struct vm_area_struct *);
412 int (*open) (struct inode *, struct file *);
413 int (*flush) (struct file *);
414 int (*release) (struct inode *, struct file *);
415 int (*fsync) (struct file *, int datasync);
416 int (*aio_fsync) (struct kiocb *, int datasync);
417 int (*fasync) (int, struct file *, int);
418 int (*lock) (struct file *, int, struct file_lock *);
419 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
420 loff_t *);
421 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
422 loff_t *);
423 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
424 void __user *);
425 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
426 loff_t *, int);
427 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
428 unsigned long, unsigned long, unsigned long);
429 int (*check_flags)(int);
430 int (*flock) (struct file *, int, struct file_lock *);
431 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
432 size_t, unsigned int);
433 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
434 size_t, unsigned int);
435 int (*setlease)(struct file *, long, struct file_lock **);
436 long (*fallocate)(struct file *, int, loff_t, loff_t);
437 };
439 locking rules:
440 All may block except for ->setlease.
441 No VFS locks held on entry except for ->fsync and ->setlease.
443 ->fsync() has i_mutex on inode.
445 ->setlease has the file_list_lock held and must not sleep.
447 ->llseek() locking has moved from llseek to the individual llseek
448 implementations. If your fs is not using generic_file_llseek, you
449 need to acquire and release the appropriate locks in your ->llseek().
450 For many filesystems, it is probably safe to acquire the inode
451 mutex or just to use i_size_read() instead.
452 Note: this does not protect the file->f_pos against concurrent modifications
453 since this is something the userspace has to take care about.
455 ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
456 Most instances call fasync_helper(), which does that maintenance, so it's
457 not normally something one needs to worry about. Return values > 0 will be
458 mapped to zero in the VFS layer.
460 ->readdir() and ->ioctl() on directories must be changed. Ideally we would
461 move ->readdir() to inode_operations and use a separate method for directory
462 ->ioctl() or kill the latter completely. One of the problems is that for
463 anything that resembles union-mount we won't have a struct file for all
464 components. And there are other reasons why the current interface is a mess...
466 ->read on directories probably must go away - we should just enforce -EISDIR
467 in sys_read() and friends.
469 --------------------------- dquot_operations -------------------------------
470 prototypes:
471 int (*write_dquot) (struct dquot *);
472 int (*acquire_dquot) (struct dquot *);
473 int (*release_dquot) (struct dquot *);
474 int (*mark_dirty) (struct dquot *);
475 int (*write_info) (struct super_block *, int);
477 These operations are intended to be more or less wrapping functions that ensure
478 a proper locking wrt the filesystem and call the generic quota operations.
480 What filesystem should expect from the generic quota functions:
482 FS recursion Held locks when called
483 write_dquot: yes dqonoff_sem or dqptr_sem
484 acquire_dquot: yes dqonoff_sem or dqptr_sem
485 release_dquot: yes dqonoff_sem or dqptr_sem
486 mark_dirty: no -
487 write_info: yes dqonoff_sem
489 FS recursion means calling ->quota_read() and ->quota_write() from superblock
490 operations.
492 More details about quota locking can be found in fs/dquot.c.
494 --------------------------- vm_operations_struct -----------------------------
495 prototypes:
496 void (*open)(struct vm_area_struct*);
497 void (*close)(struct vm_area_struct*);
498 int (*fault)(struct vm_area_struct*, struct vm_fault *);
499 int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
500 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
502 locking rules:
503 mmap_sem PageLocked(page)
504 open: yes
505 close: yes
506 fault: yes can return with page locked
507 page_mkwrite: yes can return with page locked
508 access: yes
510 ->fault() is called when a previously not present pte is about
511 to be faulted in. The filesystem must find and return the page associated
512 with the passed in "pgoff" in the vm_fault structure. If it is possible that
513 the page may be truncated and/or invalidated, then the filesystem must lock
514 the page, then ensure it is not already truncated (the page lock will block
515 subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
516 locked. The VM will unlock the page.
518 ->page_mkwrite() is called when a previously read-only pte is
519 about to become writeable. The filesystem again must ensure that there are
520 no truncate/invalidate races, and then return with the page locked. If
521 the page has been truncated, the filesystem should not look up a new page
522 like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
523 will cause the VM to retry the fault.
525 ->access() is called when get_user_pages() fails in
526 acces_process_vm(), typically used to debug a process through
527 /proc/pid/mem or ptrace. This function is needed only for
528 VM_IO | VM_PFNMAP VMAs.
530 ================================================================================
531 Dubious stuff
533 (if you break something or notice that it is broken and do not fix it yourself
534 - at least put it here)