[PATCH] fanotify: allow freeze on suspend when waiting for response from userspace

[t . vivek]

From: Vivek Trivedi <t.vivek@xxxxxxxxxxx>

If fanotify userspace response server thread is frozen first,
it may fail to send response from userspace to kernel space listener.
In this scenario, fanotify response listener will never get response
from userepace and fail to suspend.

Use freeze-friendly wait API to handle this issue.

Same problem was reported here:
https://bbs.archlinux.org/viewtopic.php?id=232270

Freezing of tasks failed after 20.005 seconds
(1 tasks refusing to freeze, wq_busy=0)

Backtrace:
[<c0582f80>] (__schedule) from [<c05835d0>] (schedule+0x4c/0xa4)
[<c0583584>] (schedule) from [<c01cb648>] (fanotify_handle_event+0x1c8/0x218)
[<c01cb480>] (fanotify_handle_event) from [<c01c8238>] (fsnotify+0x17c/0x38c)
[<c01c80bc>] (fsnotify) from [<c02676dc>] (security_file_open+0x88/0x8c)
[<c0267654>] (security_file_open) from [<c01854b0>] (do_dentry_open+0xc0/0x338)
[<c01853f0>] (do_dentry_open) from [<c0185a38>] (vfs_open+0x54/0x58)
[<c01859e4>] (vfs_open) from [<c0195480>] (do_last.isra.10+0x45c/0xcf8)
[<c0195024>] (do_last.isra.10) from [<c0196140>] (path_openat+0x424/0x600)
[<c0195d1c>] (path_openat) from [<c0197498>] (do_filp_open+0x3c/0x98)
[<c019745c>] (do_filp_open) from [<c0186b44>] (do_sys_open+0x120/0x1e4)
[<c0186a24>] (do_sys_open) from [<c0186c30>] (SyS_open+0x28/0x2c)
[<c0186c08>] (SyS_open) from [<c0010200>] (__sys_trace_return+0x0/0x20)

Signed-off-by: Kunal Shubham <k.shubham@xxxxxxxxxxx>
Signed-off-by: Vivek Trivedi <t.vivek@xxxxxxxxxxx>
---
 fs/notify/fanotify/fanotify.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 6702a6a..1d65899 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -11,6 +11,7 @@
 #include <linux/types.h>
 #include <linux/wait.h>
 #include <linux/audit.h>
+#include <linux/freezer.h>
 
 #include "fanotify.h"
 
@@ -63,7 +64,9 @@ static int fanotify_get_response(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	wait_event(group->fanotify_data.access_waitq, event->response);
+	while (!event->response)
+		wait_event_freezable(group->fanotify_data.access_waitq,
+				     event->response);
 
 	/* userspace responded, convert to something usable */
 	switch (event->response & ~FAN_AUDIT) {
-- 
1.9.1