diff options
| -rw-r--r-- | fs/file.c | 10 | ||||
| -rw-r--r-- | fs/internal.h | 1 | ||||
| -rw-r--r-- | fs/read_write.c | 13 |
3 files changed, 20 insertions, 4 deletions
diff --git a/fs/file.c b/fs/file.c index d868cdb95d1e..44efdc8c1e27 100644 --- a/fs/file.c +++ b/fs/file.c @@ -1182,6 +1182,16 @@ static inline bool file_needs_f_pos_lock(struct file *file) (file_count(file) > 1 || file->f_op->iterate_shared); } +bool file_seek_cur_needs_f_lock(struct file *file) +{ + if (!(file->f_mode & FMODE_ATOMIC_POS) && !file->f_op->iterate_shared) + return false; + + VFS_WARN_ON_ONCE((file_count(file) > 1) && + !mutex_is_locked(&file->f_pos_lock)); + return true; +} + struct fd fdget_pos(unsigned int fd) { struct fd f = fdget(fd); diff --git a/fs/internal.h b/fs/internal.h index 84607e7b05dc..1cb85a62c07f 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -338,3 +338,4 @@ static inline bool path_mounted(const struct path *path) return path->mnt->mnt_root == path->dentry; } void file_f_owner_release(struct file *file); +bool file_seek_cur_needs_f_lock(struct file *file); diff --git a/fs/read_write.c b/fs/read_write.c index a6133241dfb8..bb0ed26a0b3a 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -169,11 +169,16 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence, if (whence == SEEK_CUR) { /* - * f_lock protects against read/modify/write race with - * other SEEK_CURs. Note that parallel writes and reads - * behave like SEEK_SET. + * If the file requires locking via f_pos_lock we know + * that mutual exclusion for SEEK_CUR on the same file + * is guaranteed. If the file isn't locked, we take + * f_lock to protect against f_pos races with other + * SEEK_CURs. */ - guard(spinlock)(&file->f_lock); + if (file_seek_cur_needs_f_lock(file)) { + guard(spinlock)(&file->f_lock); + return vfs_setpos(file, file->f_pos + offset, maxsize); + } return vfs_setpos(file, file->f_pos + offset, maxsize); } |