On Fri, 18 Jun 2021 at 21:45, Sergey Shtylyov <s.shtylyov@xxxxxx> wrote: > > From: Ildar Kamaletdinov <i.kamaletdinov@xxxxxx> > > 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 <i.kamaletdinov@xxxxxx> > Signed-off-by: Sergey Shtylyov <s.shtylyov@xxxxxx> > > --- > 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(); This is just and open coded variant of wait_event_freezekillable_unsafe() which comes with this warning: /* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */ This is a really old issue and unlikely to be properly solvable with a quick hack... Thanks, Miklos
