From: Ildar Kamaletdinov <redacted>

It could be impossible to freeze the fuse task in request_wait_answer()
when it calls wait_event_killable() with the FR_FINISHED flag because
the fuse daemon could be frozen before the task, so it simply can't
finish a request. E.g. it could be impossible to freeze while doing
poll() on a fuse FS:

[   90.468003] (0)[]Freezing of tasks aborted after 6.507 seconds
[   90.468793] (0)[1649:kworker/u8:18]qtaround::mt::A D
[   90.468830]    0  1590   1102 0x00400009
[   90.468850] (0)[1649:kworker/u8:18]Call trace:
[   90.468887] (0)[1649:kworker/u8:18][<ffffff82a7685a44>] __switch_to+0xd8/0xf4
[   90.468929] (0)[1649:kworker/u8:18][<ffffff82a851fa9c>] __schedule+0x75c/0x964
[   90.468964] (0)[1649:kworker/u8:18][<ffffff82a851fd14>] schedule+0x70/0x90
[   90.468995] (0)[1649:kworker/u8:18][<ffffff82a79fec00>] __fuse_request_send+0x228/0x3a4
[   90.469031] (0)[1649:kworker/u8:18][<ffffff82a79feeec>] fuse_simple_request+0x170/0x1c4
[   90.469068] (0)[1649:kworker/u8:18][<ffffff82a7a070e0>] fuse_file_poll+0x164/0x1c8
[   90.469107] (0)[1649:kworker/u8:18][<ffffff82a7851050>] do_sys_poll+0x2f4/0x5a0
[   90.469142] (0)[1649:kworker/u8:18][<ffffff82a78518f4>] do_restart_poll+0x4c/0x90
[   90.469178] (0)[1649:kworker/u8:18][<ffffff82a76bb32c>] sys_restart_syscall+0x18/0x20
[   90.469213] (0)[1649:kworker/u8:18][<ffffff82a76835c0>] el0_svc_naked+0x34/0x38
[   90.469457] (3)[647:dsme-server]Restarting tasks ...

Use freezer_do_not_count() to tell freezer to ignore the task while it
waits for event.

[Sergey: added #include <linux/freezer.h>, cleaned up the patch description]

Link: https://bugzilla.kernel.org/show_bug.cgi?id=198879
Fixes: 7d3a07fcb8a0 (fuse: don't mess with blocking signals)
Signed-off-by: Ildar Kamaletdinov <redacted>
Signed-off-by: Sergey Shtylyov <redacted>

---
This patch is against the Linus' repo -- I didn't find a tag suitable for
the fixes in Miklos Szeredi's FUSE repo. :-(

 fs/fuse/dev.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux/fs/fuse/dev.c
===================================================================

--- linux.orig/fs/fuse/dev.c
+++ linux/fs/fuse/dev.c

@@ -8,6 +8,7 @@

 #include "fuse_i.h"

+#include <linux/freezer.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/poll.h>

@@ -386,9 +387,11 @@ static void request_wait_answer(struct f
        }

        if (!test_bit(FR_FORCE, &req->flags)) {
+               freezer_do_not_count();
                /* Only fatal signals may interrupt this */
                err = wait_event_killable(req->waitq,
                                        test_bit(FR_FINISHED, &req->flags));
+               freezer_count();