Patch "fsnotify: optimize FS_MODIFY events with no ignored masks" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    fsnotify: optimize FS_MODIFY events with no ignored masks

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fsnotify-optimize-fs_modify-events-with-no-ignored-m.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e901bc3c152f1667701c5c6b8e9b40fb564f5e65
Author: Amir Goldstein <amir73il@xxxxxxxxx>
Date:   Wed Feb 23 17:14:38 2022 +0200

    fsnotify: optimize FS_MODIFY events with no ignored masks
    
    [ Upstream commit 04e317ba72d07901b03399b3d1525e83424df5b3 ]
    
    fsnotify() treats FS_MODIFY events specially - it does not skip them
    even if the FS_MODIFY event does not apear in the object's fsnotify
    mask.  This is because send_to_group() checks if FS_MODIFY needs to
    clear ignored mask of marks.
    
    The common case is that an object does not have any mark with ignored
    mask and in particular, that it does not have a mark with ignored mask
    and without the FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY flag.
    
    Set FS_MODIFY in object's fsnotify mask during fsnotify_recalc_mask()
    if object has a mark with an ignored mask and without the
    FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY flag and remove the special
    treatment of FS_MODIFY in fsnotify(), so that FS_MODIFY events could
    be optimized in the common case.
    
    Call fsnotify_recalc_mask() from fanotify after adding or removing an
    ignored mask from a mark without FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY
    or when adding the FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY flag to a mark
    with ignored mask (the flag cannot be removed by fanotify uapi).
    
    Performance results for doing 10000000 write(2)s to tmpfs:
    
                                    vanilla         patched
    without notification mark       25.486+-1.054   24.965+-0.244
    with notification mark          30.111+-0.139   26.891+-1.355
    
    So we can see the overhead of notification subsystem has been
    drastically reduced.
    
    Link: https://lore.kernel.org/r/20220223151438.790268-3-amir73il@xxxxxxxxx
    Suggested-by: Jan Kara <jack@xxxxxxx>
    Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
    Signed-off-by: Jan Kara <jack@xxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 12fb209e60419..64abec874d8e3 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1069,8 +1069,28 @@ static int fanotify_remove_inode_mark(struct fsnotify_group *group,
 				    flags, umask);
 }
 
+static void fanotify_mark_add_ignored_mask(struct fsnotify_mark *fsn_mark,
+					   __u32 mask, unsigned int flags,
+					   __u32 *removed)
+{
+	fsn_mark->ignored_mask |= mask;
+
+	/*
+	 * Setting FAN_MARK_IGNORED_SURV_MODIFY for the first time may lead to
+	 * the removal of the FS_MODIFY bit in calculated mask if it was set
+	 * because of an ignored mask that is now going to survive FS_MODIFY.
+	 */
+	if ((flags & FAN_MARK_IGNORED_SURV_MODIFY) &&
+	    !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY)) {
+		fsn_mark->flags |= FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY;
+		if (!(fsn_mark->mask & FS_MODIFY))
+			*removed = FS_MODIFY;
+	}
+}
+
 static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
-				       __u32 mask, unsigned int flags)
+				       __u32 mask, unsigned int flags,
+				       __u32 *removed)
 {
 	__u32 oldmask, newmask;
 
@@ -1079,9 +1099,7 @@ static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
 	if (!(flags & FAN_MARK_IGNORED_MASK)) {
 		fsn_mark->mask |= mask;
 	} else {
-		fsn_mark->ignored_mask |= mask;
-		if (flags & FAN_MARK_IGNORED_SURV_MODIFY)
-			fsn_mark->flags |= FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY;
+		fanotify_mark_add_ignored_mask(fsn_mark, mask, flags, removed);
 	}
 	newmask = fsnotify_calc_mask(fsn_mark);
 	spin_unlock(&fsn_mark->lock);
@@ -1144,7 +1162,7 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 			     __kernel_fsid_t *fsid)
 {
 	struct fsnotify_mark *fsn_mark;
-	__u32 added;
+	__u32 added, removed = 0;
 	int ret = 0;
 
 	mutex_lock(&group->mark_mutex);
@@ -1167,8 +1185,8 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 			goto out;
 	}
 
-	added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
-	if (added & ~fsnotify_conn_mask(fsn_mark->connector))
+	added = fanotify_mark_add_to_mask(fsn_mark, mask, flags, &removed);
+	if (removed || (added & ~fsnotify_conn_mask(fsn_mark->connector)))
 		fsnotify_recalc_mask(fsn_mark->connector);
 
 out:
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ab81a0776ece5..494f653efbc6e 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -531,11 +531,13 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 
 
 	/*
-	 * if this is a modify event we may need to clear the ignored masks
-	 * otherwise return if none of the marks care about this type of event.
+	 * If this is a modify event we may need to clear some ignored masks.
+	 * In that case, the object with ignored masks will have the FS_MODIFY
+	 * event in its mask.
+	 * Otherwise, return if none of the marks care about this type of event.
 	 */
 	test_mask = (mask & ALL_FSNOTIFY_EVENTS);
-	if (!(mask & FS_MODIFY) && !(test_mask & marks_mask))
+	if (!(test_mask & marks_mask))
 		return 0;
 
 	iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 5f9c960049b07..0805b74cae441 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -609,6 +609,10 @@ static inline __u32 fsnotify_calc_mask(struct fsnotify_mark *mark)
 	if (!mark->ignored_mask)
 		return mask;
 
+	/* Interest in FS_MODIFY may be needed for clearing ignored mask */
+	if (!(mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
+		mask |= FS_MODIFY;
+
 	/*
 	 * If mark is interested in ignoring events on children, the object must
 	 * show interest in those events for fsnotify_parent() to notice it.




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