Messages in this thread | | | Date | Mon, 2 Feb 2015 16:29:44 +1100 | From | Dave Chinner <> | Subject | Re: [GIT PULL] aio: fix sleeping while TASK_INTERRUPTIBLE |
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On Sun, Feb 01, 2015 at 05:18:17PM -0800, Linus Torvalds wrote: > On Sun, Feb 1, 2015 at 4:16 PM, Benjamin LaHaise <bcrl@kvack.org> wrote: > >> > >> What's the bug you think could happen? > > > > The bug would be in code that gets run via mutex_lock(), kmap(), or (more > > likely) in the random mm or filesystem code that could be invoked via > > copy_to_user(). > > Ahh. That would be a bug, yes, but it wouldn't be one in the aio code. > > If somebody just does a "schedule()" and thinks that their own private > events are the only thing that can wake it up, and doesn't use one of > the millions of "wait_event_xyz()" variations to actually wait for the > real completion, that is just buggy. Always. Always has been. > > So I wouldn't worry too much about it. It has never been correct to do > that, and it's not one of the standard patterns for sleeping anyway. > Which is not to say that it might not exist in some dank corner of the > kernel, of course, but you shouldn't write code trying to make buggy > code like that happy. If we ever find code like that, let's just fix > it where the bug exists, not try to write odd code in places where it > isn't. > > And I'd actually be a bit surprised to see that kind of really broken > code. You really almost have to work at it. All our normal "sleep > until X" patterns are much more obvious, and it's just _simpler_ to do > the right thing with "wait_event()" than to mis-code an explicit "set > task state and then just schedule without actually checking the thing > you are waiting for".
So what's the outcome here? I'm running v3.19-rc7 kernel and xfstests::generic/036 is still tripping this warning from the aio code:
[ 23.920785] run fstests generic/036 at 2015-02-02 16:13:01 [ 24.168001] xfs_io (4814) used greatest stack depth: 11640 bytes left [ 24.187061] ------------[ cut here ]------------ [ 24.187071] WARNING: CPU: 1 PID: 4820 at kernel/sched/core.c:7300 __might_sleep+0x7f/0x90() [ 24.187076] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff810d85a3>] prepare_to_wait_event+0x63/0x110 [ 24.187078] Modules linked in: [ 24.187080] CPU: 1 PID: 4820 Comm: aio-dio-fcntl-r Not tainted 3.19.0-rc7-dgc+ #706 [ 24.187081] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 [ 24.187084] ffffffff821c0372 ffff8800b84d3cd8 ffffffff81daf2bd 0000000000008c8c [ 24.187085] ffff8800b84d3d28 ffff8800b84d3d18 ffffffff8109beda ffff8800b84d3cf8 [ 24.187087] ffffffff821c115e 0000000000000061 0000000000000000 00007fff38e95180 [ 24.187087] Call Trace: [ 24.187093] [<ffffffff81daf2bd>] dump_stack+0x4c/0x65 [ 24.187096] [<ffffffff8109beda>] warn_slowpath_common+0x8a/0xc0 [ 24.187099] [<ffffffff8109bf56>] warn_slowpath_fmt+0x46/0x50 [ 24.187101] [<ffffffff810d85a3>] ? prepare_to_wait_event+0x63/0x110 [ 24.187103] [<ffffffff810d85a3>] ? prepare_to_wait_event+0x63/0x110 [ 24.187104] [<ffffffff810bdfcf>] __might_sleep+0x7f/0x90 [ 24.187107] [<ffffffff81db8344>] mutex_lock+0x24/0x45 [ 24.187111] [<ffffffff81216b7c>] aio_read_events+0x4c/0x290 [ 24.187113] [<ffffffff81216fac>] read_events+0x1ec/0x220 [ 24.187115] [<ffffffff810d8650>] ? prepare_to_wait_event+0x110/0x110 [ 24.187119] [<ffffffff810fdb10>] ? hrtimer_get_res+0x50/0x50 [ 24.187121] [<ffffffff8121899d>] SyS_io_getevents+0x4d/0xb0 [ 24.187124] [<ffffffff81130b16>] ? __audit_syscall_exit+0x236/0x2e0 [ 24.187127] [<ffffffff81dba5a9>] system_call_fastpath+0x12/0x17 [ 24.187128] ---[ end trace 9f078e8e19f765dd ]---
This test does a aio write loop with a single outstanding event. i.e:
while (1) { io_prep_pwrite(&iocb, fd, buf, BUF_SIZE, BUF_SIZE); err = io_submit(ctx, 1, iocbs); if (err) ..... err = io_getevents(ctx, 1, 1, &ev, NULL); ..... }
The kernel should not be throwing warnings on basic regression tests, so something needs to be fixed...
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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