diff options
Diffstat (limited to 'Documentation/filesystems/locking.rst')
| -rw-r--r-- | Documentation/filesystems/locking.rst | 176 |
1 files changed, 76 insertions, 100 deletions
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 4bb2627026ec..2e567e341c3b 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -17,7 +17,8 @@ dentry_operations prototypes:: - int (*d_revalidate)(struct dentry *, unsigned int); + int (*d_revalidate)(struct inode *, const struct qstr *, + struct dentry *, unsigned int); int (*d_weak_revalidate)(struct dentry *, unsigned int); int (*d_hash)(const struct dentry *, struct qstr *); int (*d_compare)(const struct dentry *, @@ -29,7 +30,9 @@ prototypes:: char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen); struct vfsmount *(*d_automount)(struct path *path); int (*d_manage)(const struct path *, bool); - struct dentry *(*d_real)(struct dentry *, const struct inode *); + struct dentry *(*d_real)(struct dentry *, enum d_real_type type); + bool (*d_unalias_trylock)(const struct dentry *); + void (*d_unalias_unlock)(const struct dentry *); locking rules: @@ -49,6 +52,8 @@ d_dname: no no no no d_automount: no no yes no d_manage: no no yes (ref-walk) maybe d_real no no yes no +d_unalias_trylock yes no no no +d_unalias_unlock yes no no no ================== =========== ======== ============== ======== inode_operations @@ -56,40 +61,43 @@ inode_operations prototypes:: - int (*create) (struct inode *,struct dentry *,umode_t, bool); + int (*create) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t, bool); struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int); int (*link) (struct dentry *,struct inode *,struct dentry *); int (*unlink) (struct inode *,struct dentry *); - int (*symlink) (struct inode *,struct dentry *,const char *); - int (*mkdir) (struct inode *,struct dentry *,umode_t); + int (*symlink) (struct mnt_idmap *, struct inode *,struct dentry *,const char *); + struct dentry *(*mkdir) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t); int (*rmdir) (struct inode *,struct dentry *); - int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t); - int (*rename) (struct inode *, struct dentry *, + int (*mknod) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t,dev_t); + int (*rename) (struct mnt_idmap *, struct inode *, struct dentry *, struct inode *, struct dentry *, unsigned int); int (*readlink) (struct dentry *, char __user *,int); const char *(*get_link) (struct dentry *, struct inode *, struct delayed_call *); void (*truncate) (struct inode *); - int (*permission) (struct inode *, int, unsigned int); - struct posix_acl * (*get_acl)(struct inode *, int, bool); - int (*setattr) (struct dentry *, struct iattr *); - int (*getattr) (const struct path *, struct kstat *, u32, unsigned int); + int (*permission) (struct mnt_idmap *, struct inode *, int, unsigned int); + struct posix_acl * (*get_inode_acl)(struct inode *, int, bool); + int (*setattr) (struct mnt_idmap *, struct dentry *, struct iattr *); + int (*getattr) (struct mnt_idmap *, const struct path *, struct kstat *, u32, unsigned int); ssize_t (*listxattr) (struct dentry *, char *, size_t); int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len); void (*update_time)(struct inode *, struct timespec *, int); int (*atomic_open)(struct inode *, struct dentry *, struct file *, unsigned open_flag, umode_t create_mode); - int (*tmpfile) (struct inode *, struct dentry *, umode_t); - int (*fileattr_set)(struct user_namespace *mnt_userns, + int (*tmpfile) (struct mnt_idmap *, struct inode *, + struct file *, umode_t); + int (*fileattr_set)(struct mnt_idmap *idmap, struct dentry *dentry, struct fileattr *fa); int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); + struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int); + struct offset_ctx *(*get_offset_ctx)(struct inode *inode); locking rules: all may block -============= ============================================= +============== ================================================== ops i_rwsem(inode) -============= ============================================= +============== ================================================== lookup: shared create: exclusive link: exclusive (both) @@ -98,11 +106,12 @@ symlink: exclusive mkdir: exclusive unlink: exclusive (both) rmdir: exclusive (both)(see below) -rename: exclusive (all) (see below) +rename: exclusive (both parents, some children) (see below) readlink: no get_link: no setattr: exclusive permission: no (may not block if called in rcu-walk mode) +get_inode_acl: no get_acl: no getattr: no listxattr: no @@ -112,12 +121,16 @@ atomic_open: shared (exclusive if O_CREAT is set in open flags) tmpfile: no fileattr_get: no or exclusive fileattr_set: exclusive -============= ============================================= +get_offset_ctx no +============== ================================================== Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem exclusive on victim. cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem. + ->unlink() and ->rename() have ->i_rwsem exclusive on all non-directories + involved. + ->rename() has ->i_rwsem exclusive on any subdirectory that changes parent. See Documentation/filesystems/directory-locking.rst for more detailed discussion of the locking scheme for directory operations. @@ -132,7 +145,7 @@ prototypes:: struct inode *inode, const char *name, void *buffer, size_t size); int (*set)(const struct xattr_handler *handler, - struct user_namespace *mnt_userns, + struct mnt_idmap *idmap, struct dentry *dentry, struct inode *inode, const char *name, const void *buffer, size_t size, int flags); @@ -236,17 +249,16 @@ address_space_operations ======================== prototypes:: - int (*writepage)(struct page *page, struct writeback_control *wbc); int (*read_folio)(struct file *, struct folio *); int (*writepages)(struct address_space *, struct writeback_control *); bool (*dirty_folio)(struct address_space *, struct folio *folio); void (*readahead)(struct readahead_control *); int (*write_begin)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, - struct page **pagep, void **fsdata); + struct folio **foliop, void **fsdata); int (*write_end)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied, - struct page *page, void *fsdata); + struct folio *folio, void *fsdata); sector_t (*bmap)(struct address_space *, sector_t); void (*invalidate_folio) (struct folio *, size_t start, size_t len); bool (*release_folio)(struct folio *, gfp_t); @@ -256,7 +268,7 @@ prototypes:: struct folio *src, enum migrate_mode); int (*launder_folio)(struct folio *); bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count); - int (*error_remove_page)(struct address_space *, struct page *); + int (*error_remove_folio)(struct address_space *, struct folio *); int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span) int (*swap_deactivate)(struct file *); int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter); @@ -267,12 +279,11 @@ locking rules: ====================== ======================== ========= =============== ops folio locked i_rwsem invalidate_lock ====================== ======================== ========= =============== -writepage: yes, unlocks (see below) read_folio: yes, unlocks shared writepages: dirty_folio: maybe readahead: yes, unlocks shared -write_begin: locks the page exclusive +write_begin: locks the folio exclusive write_end: yes, unlocks exclusive bmap: invalidate_folio: yes exclusive @@ -282,7 +293,7 @@ direct_IO: migrate_folio: yes (both) launder_folio: yes is_partially_uptodate: yes -error_remove_page: yes +error_remove_folio: yes swap_activate: no swap_deactivate: no swap_rw: yes, unlocks @@ -296,54 +307,6 @@ completion. ->readahead() unlocks the folios that I/O is attempted on like ->read_folio(). -->writepage() is used for two purposes: for "memory cleansing" and for -"sync". These are quite different operations and the behaviour may differ -depending upon the mode. - -If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then -it *must* start I/O against the page, even if that would involve -blocking on in-progress I/O. - -If writepage is called for memory cleansing (sync_mode == -WBC_SYNC_NONE) then its role is to get as much writeout underway as -possible. So writepage should try to avoid blocking against -currently-in-progress I/O. - -If the filesystem is not called for "sync" and it determines that it -would need to block against in-progress I/O to be able to start new I/O -against the page the filesystem should redirty the page with -redirty_page_for_writepage(), then unlock the page and return zero. -This may also be done to avoid internal deadlocks, but rarely. - -If the filesystem is called for sync then it must wait on any -in-progress I/O and then start new I/O. - -The filesystem should unlock the page synchronously, before returning to the -caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE -value. WRITEPAGE_ACTIVATE means that page cannot really be written out -currently, and VM should stop calling ->writepage() on this page for some -time. VM does this by moving page to the head of the active list, hence the -name. - -Unless the filesystem is going to redirty_page_for_writepage(), unlock the page -and return zero, writepage *must* run set_page_writeback() against the page, -followed by unlocking it. Once set_page_writeback() has been run against the -page, write I/O can be submitted and the write I/O completion handler must run -end_page_writeback() once the I/O is complete. If no I/O is submitted, the -filesystem must run end_page_writeback() against the page before returning from -writepage. - -That is: after 2.5.12, pages which are under writeout are *not* locked. Note, -if the filesystem needs the page to be locked during writeout, that is ok, too, -the page is allowed to be unlocked at any point in time between the calls to -set_page_writeback() and end_page_writeback(). - -Note, failure to run either redirty_page_for_writepage() or the combination of -set_page_writeback()/end_page_writeback() on a page submitted to writepage -will leave the page itself marked clean but it will be tagged as dirty in the -radix tree. This incoherency can lead to all sorts of hard-to-debug problems -in the filesystem like having dirty inodes at umount and losing written data. - ->writepages() is used for periodic writeback and for syscall-initiated sync operations. The address_space should start I/O against at least ``*nr_to_write`` pages. ``*nr_to_write`` must be decremented for each page @@ -351,8 +314,8 @@ which is written. The address_space implementation may write more (or less) pages than ``*nr_to_write`` asks for, but it should try to be reasonably close. If nr_to_write is NULL, all dirty pages must be written. -writepages should _only_ write pages which are present on -mapping->io_pages. +writepages should _only_ write pages which are present in +mapping->i_pages. ->dirty_folio() is called from various places in the kernel when the target folio is marked as needing writeback. The folio cannot be @@ -371,10 +334,17 @@ invalidate_lock before invalidating page cache in truncate / hole punch path (and thus calling into ->invalidate_folio) to block races between page cache invalidation and page cache filling functions (fault, read, ...). -->release_folio() is called when the kernel is about to try to drop the -buffers from the folio in preparation for freeing it. It returns false to -indicate that the buffers are (or may be) freeable. If ->release_folio is -NULL, the kernel assumes that the fs has no private interest in the buffers. +->release_folio() is called when the MM wants to make a change to the +folio that would invalidate the filesystem's private data. For example, +it may be about to be removed from the address_space or split. The folio +is locked and not under writeback. It may be dirty. The gfp parameter +is not usually used for allocation, but rather to indicate what the +filesystem may do to attempt to free the private data. The filesystem may +return false to indicate that the folio's private data cannot be freed. +If it returns true, it should have already removed the private data from +the folio. If a filesystem does not provide a ->release_folio method, +the pagecache will assume that private data is buffer_heads and call +try_to_free_buffers(). ->free_folio() is called when the kernel has dropped the folio from the page cache. @@ -506,7 +476,6 @@ prototypes:: ssize_t (*read_iter) (struct kiocb *, struct iov_iter *); ssize_t (*write_iter) (struct kiocb *, struct iov_iter *); int (*iopoll) (struct kiocb *kiocb, bool spin); - int (*iterate) (struct file *, struct dir_context *); int (*iterate_shared) (struct file *, struct dir_context *); __poll_t (*poll) (struct file *, struct poll_table_struct *); long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); @@ -518,8 +487,6 @@ prototypes:: int (*fsync) (struct file *, loff_t start, loff_t end, int datasync); int (*fasync) (int, struct file *, int); int (*lock) (struct file *, int, struct file_lock *); - ssize_t (*sendpage) (struct file *, struct page *, int, size_t, - loff_t *, int); unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long); int (*check_flags)(int); @@ -550,9 +517,8 @@ 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. -->iterate() is called with i_rwsem exclusive. - -->iterate_shared() is called with i_rwsem at least shared. +->iterate_shared() is called with i_rwsem held for reading, and with the +file f_pos_lock held exclusively ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags. Most instances call fasync_helper(), which does that maintenance, so it's @@ -627,26 +593,29 @@ vm_operations_struct prototypes:: - void (*open)(struct vm_area_struct*); - void (*close)(struct vm_area_struct*); - vm_fault_t (*fault)(struct vm_area_struct*, struct vm_fault *); + void (*open)(struct vm_area_struct *); + void (*close)(struct vm_area_struct *); + vm_fault_t (*fault)(struct vm_fault *); + vm_fault_t (*huge_fault)(struct vm_fault *, unsigned int order); + vm_fault_t (*map_pages)(struct vm_fault *, pgoff_t start, pgoff_t end); vm_fault_t (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *); vm_fault_t (*pfn_mkwrite)(struct vm_area_struct *, struct vm_fault *); int (*access)(struct vm_area_struct *, unsigned long, void*, int, int); locking rules: -============= ========= =========================== +============= ========== =========================== ops mmap_lock PageLocked(page) -============= ========= =========================== -open: yes -close: yes -fault: yes can return with page locked -map_pages: yes -page_mkwrite: yes can return with page locked -pfn_mkwrite: yes -access: yes -============= ========= =========================== +============= ========== =========================== +open: write +close: read/write +fault: read can return with page locked +huge_fault: maybe-read +map_pages: maybe-read +page_mkwrite: read can return with page locked +pfn_mkwrite: read +access: read +============= ========== =========================== ->fault() is called when a previously not present pte is about to be faulted in. The filesystem must find and return the page associated with the passed in @@ -656,11 +625,18 @@ then ensure the page is not already truncated (invalidate_lock will block subsequent truncate), and then return with VM_FAULT_LOCKED, and the page locked. The VM will unlock the page. +->huge_fault() is called when there is no PUD or PMD entry present. This +gives the filesystem the opportunity to install a PUD or PMD sized page. +Filesystems can also use the ->fault method to return a PMD sized page, +so implementing this function may not be necessary. In particular, +filesystems should not call filemap_fault() from ->huge_fault(). +The mmap_lock may not be held when this method is called. + ->map_pages() is called when VM asks to map easy accessible pages. Filesystem should find and map pages associated with offsets from "start_pgoff" -till "end_pgoff". ->map_pages() is called with page table locked and must +till "end_pgoff". ->map_pages() is called with the RCU lock held and must not block. If it's not possible to reach a page without blocking, -filesystem should skip it. Filesystem should use do_set_pte() to setup +filesystem should skip it. Filesystem should use set_pte_range() to setup page table entry. Pointer to entry associated with the page is passed in "pte" field in vm_fault structure. Pointers to entries for other offsets should be calculated relative to "pte". |