linux-kernel - [PATCH] fanotify: Make wait for permission events interruptible

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Date:   Thu, 21 Mar 2019 16:11:42 +0100
From:   Jan Kara <jack@...e.cz>
To:     <linux-fsdevel@...r.kernel.org>
Cc:     Orion Poplawski <orion@...a.com>,
        Vivek Trivedi <t.vivek@...sung.com>,
        Amir Goldstein <amir73il@...il.com>,
        <linux-api@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH] fanotify: Make wait for permission events interruptible

Switch waiting for response to fanotify permission events interruptible.
This allows e.g. the system to be suspended while there are some
fanotify permission events pending (which is reportedly pretty common
when for example AV solution is in use). However just making the wait
interruptible can result in e.g. open(2) returning -EINTR where
previously such error code never happened in practice. To avoid
confusion of userspace due to this error code, return -ERESTARTNOINTR
instead.

Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/notify/fanotify/fanotify.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Orion, can you give this patch some testing with your usecase? Also if anybody
sees any issue with returning -ERESTARTNOINTR I have missed, please speak up.

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 6b9c27548997..eb790853844b 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -92,10 +92,17 @@ static int fanotify_get_response(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	ret = wait_event_killable(group->fanotify_data.access_waitq,
-				  event->state == FAN_EVENT_ANSWERED);
+	ret = wait_event_interruptible(group->fanotify_data.access_waitq,
+				       event->state == FAN_EVENT_ANSWERED);
 	/* Signal pending? */
 	if (ret < 0) {
+		/*
+		 * Force restarting a syscall so that this is mostly invisible
+		 * for userspace which is not prepared for handling EINTR e.g.
+		 * from open(2).
+		 */
+		if (ret == -ERESTARTSYS)
+			ret = -ERESTARTNOINTR;
 		spin_lock(&group->notification_lock);
 		/* Event reported to userspace and no answer yet? */
 		if (event->state == FAN_EVENT_REPORTED) {
-- 
2.16.4