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fsnotify: optimize FMODE_NONOTIFY_PERM for the common cases 

The most unlikely watched permission event is FAN_ACCESS_PERM, because
at the time that it was introduced there were no evictable ignore mark,
so subscribing to FAN_ACCESS_PERM would have incured a very high
overhead.

Yet, when we set the fmode to FMODE_NOTIFY_HSM(), we never skip trying
to send FAN_ACCESS_PERM, which is almost always a waste of cycles.

We got to this logic because of bundling FAN_OPEN*_PERM and
FAN_ACCESS_PERM in the same category and because FAN_OPEN_PERM is a
commonly used event.

By open coding fsnotify_open_perm() in fsnotify_open_perm_and_set_mode(),
we no longer need to regard FAN_OPEN*_PERM when calculating fmode.

This leaves the case of having pre-content events and not having any
other permission event in the object masks a more likely case than the
other way around.

Rework the fmode macros and code so that their meaning now refers only
to hooks on an already open file:

- FMODE_NOTIFY_NONE()		skip all events
- FMODE_NOTIFY_ACCESS_PERM()	send all permission events including
  				FAN_ACCESS_PERM
- FMODE_NOTIFY_HSM()		send pre-content permission events

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250708143641.418603-3-amir73il@gmail.com
pull/1310/head
Amir Goldstein 2025-07-08 16:36:41 +02:00 committed by Jan Kara
parent 08da98e1b2
commit 0d4c4d4ea4
3 changed files with 53 additions and 61 deletions
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75
fs/notify/fsnotify.c
View File

@ -199,8 +199,8 @@ static bool fsnotify_event_needs_parent(struct inode *inode, __u32 mnt_mask,
}
/* Are there any inode/mount/sb objects that watch for these events? */
static inline bool fsnotify_object_watched(struct inode *inode, __u32 mnt_mask,
__u32 mask)
static inline __u32 fsnotify_object_watched(struct inode *inode, __u32 mnt_mask,
__u32 mask)
{
__u32 marks_mask = READ_ONCE(inode->i_fsnotify_mask) | mnt_mask |
READ_ONCE(inode->i_sb->s_fsnotify_mask);
@ -665,7 +665,7 @@ int fsnotify_open_perm_and_set_mode(struct file *file)
{
struct dentry *dentry = file->f_path.dentry, *parent;
struct super_block *sb = dentry->d_sb;
__u32 mnt_mask, p_mask;
__u32 mnt_mask, p_mask = 0;
/* Is it a file opened by fanotify? */
if (FMODE_FSNOTIFY_NONE(file->f_mode))
@ -683,45 +683,60 @@ int fsnotify_open_perm_and_set_mode(struct file *file)
}
/*
* If there are permission event watchers but no pre-content event
* watchers, set FMODE_NONOTIFY | FMODE_NONOTIFY_PERM to indicate that.
* OK, there are some permission event watchers. Check if anybody is
* watching for permission events on *this* file.
*/
if ((!d_is_dir(dentry) && !d_is_reg(dentry)) ||
likely(!fsnotify_sb_has_priority_watchers(sb,
FSNOTIFY_PRIO_PRE_CONTENT))) {
file_set_fsnotify_mode(file, FMODE_NONOTIFY |
FMODE_NONOTIFY_PERM);
goto open_perm;
mnt_mask = READ_ONCE(real_mount(file->f_path.mnt)->mnt_fsnotify_mask);
p_mask = fsnotify_object_watched(d_inode(dentry), mnt_mask,
ALL_FSNOTIFY_PERM_EVENTS);
if (dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED) {
parent = dget_parent(dentry);
p_mask |= fsnotify_inode_watches_children(d_inode(parent));
dput(parent);
}
/*
* OK, there are some pre-content watchers. Check if anybody is
* watching for pre-content events on *this* file.
* Legacy FAN_ACCESS_PERM events have very high performance overhead,
* so unlikely to be used in the wild. If they are used there will be
* no optimizations at all.
*/
mnt_mask = READ_ONCE(real_mount(file->f_path.mnt)->mnt_fsnotify_mask);
if (unlikely(fsnotify_object_watched(d_inode(dentry), mnt_mask,
FSNOTIFY_PRE_CONTENT_EVENTS))) {
/* Enable pre-content events */
if (unlikely(p_mask & FS_ACCESS_PERM)) {
/* Enable all permission and pre-content events */
file_set_fsnotify_mode(file, 0);
goto open_perm;
}
/* Is parent watching for pre-content events on this file? */
if (dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED) {
parent = dget_parent(dentry);
p_mask = fsnotify_inode_watches_children(d_inode(parent));
dput(parent);
if (p_mask & FSNOTIFY_PRE_CONTENT_EVENTS) {
/* Enable pre-content events */
file_set_fsnotify_mode(file, 0);
goto open_perm;
}
/*
* Pre-content events are only supported on regular files.
* If there are pre-content event watchers and no permission access
* watchers, set FMODE_NONOTIFY | FMODE_NONOTIFY_PERM to indicate that.
* That is the common case with HSM service.
*/
if (d_is_reg(dentry) && (p_mask & FSNOTIFY_PRE_CONTENT_EVENTS)) {
file_set_fsnotify_mode(file, FMODE_NONOTIFY |
FMODE_NONOTIFY_PERM);
goto open_perm;
}
/* Nobody watching for pre-content events from this file */
file_set_fsnotify_mode(file, FMODE_NONOTIFY | FMODE_NONOTIFY_PERM);
/* Nobody watching permission and pre-content events on this file */
file_set_fsnotify_mode(file, FMODE_NONOTIFY_PERM);
open_perm:
return fsnotify_open_perm(file);
/*
* Send open perm events depending on object masks and regardless of
* FMODE_NONOTIFY_PERM.
*/
if (file->f_flags & __FMODE_EXEC && p_mask & FS_OPEN_EXEC_PERM) {
int ret = fsnotify_path(&file->f_path, FS_OPEN_EXEC_PERM);
if (ret)
return ret;
}
if (p_mask & FS_OPEN_PERM)
return fsnotify_path(&file->f_path, FS_OPEN_PERM);
return 0;
}
#endif

12
include/linux/fs.h
View File

@ -200,12 +200,12 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/*
* The two FMODE_NONOTIFY* define which fsnotify events should not be generated
* for a file. These are the possible values of (f->f_mode &
* FMODE_FSNOTIFY_MASK) and their meaning:
* for an open file. These are the possible values of
* (f->f_mode & FMODE_FSNOTIFY_MASK) and their meaning:
*
* FMODE_NONOTIFY - suppress all (incl. non-permission) events.
* FMODE_NONOTIFY_PERM - suppress permission (incl. pre-content) events.
* FMODE_NONOTIFY | FMODE_NONOTIFY_PERM - suppress only pre-content events.
* FMODE_NONOTIFY | FMODE_NONOTIFY_PERM - suppress only FAN_ACCESS_PERM.
*/
#define FMODE_FSNOTIFY_MASK \
(FMODE_NONOTIFY | FMODE_NONOTIFY_PERM)
@ -213,13 +213,13 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
#define FMODE_FSNOTIFY_NONE(mode) \
((mode & FMODE_FSNOTIFY_MASK) == FMODE_NONOTIFY)
#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
#define FMODE_FSNOTIFY_PERM(mode) \
#define FMODE_FSNOTIFY_HSM(mode) \
((mode & FMODE_FSNOTIFY_MASK) == 0 || \
(mode & FMODE_FSNOTIFY_MASK) == (FMODE_NONOTIFY | FMODE_NONOTIFY_PERM))
#define FMODE_FSNOTIFY_HSM(mode) \
#define FMODE_FSNOTIFY_ACCESS_PERM(mode) \
((mode & FMODE_FSNOTIFY_MASK) == 0)
#else
#define FMODE_FSNOTIFY_PERM(mode) 0
#define FMODE_FSNOTIFY_ACCESS_PERM(mode) 0
#define FMODE_FSNOTIFY_HSM(mode) 0
#endif

27
include/linux/fsnotify.h
View File

@ -147,9 +147,6 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
if (!(perm_mask & (MAY_READ | MAY_WRITE | MAY_ACCESS)))
return 0;
if (likely(!FMODE_FSNOTIFY_PERM(file->f_mode)))
return 0;
/*
* read()/write() and other types of access generate pre-content events.
*/
@ -160,7 +157,8 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
return ret;
}
if (!(perm_mask & MAY_READ))
if (!(perm_mask & MAY_READ) ||
likely(!FMODE_FSNOTIFY_ACCESS_PERM(file->f_mode)))
return 0;
/*
@ -208,22 +206,6 @@ static inline int fsnotify_file_perm(struct file *file, int perm_mask)
return fsnotify_file_area_perm(file, perm_mask, NULL, 0);
}
/*
* fsnotify_open_perm - permission hook before file open
*/
static inline int fsnotify_open_perm(struct file *file)
{
int ret;
if (file->f_flags & __FMODE_EXEC) {
ret = fsnotify_path(&file->f_path, FS_OPEN_EXEC_PERM);
if (ret)
return ret;
}
return fsnotify_path(&file->f_path, FS_OPEN_PERM);
}
#else
static inline int fsnotify_open_perm_and_set_mode(struct file *file)
{
@ -251,11 +233,6 @@ static inline int fsnotify_file_perm(struct file *file, int perm_mask)
{
return 0;
}
static inline int fsnotify_open_perm(struct file *file)
{
return 0;
}
#endif
/*