On Wed, 25 Feb 2015 11:13:18 +0100 Thomas Huth <thuth@xxxxxxxxxxxxxxxxxx> wrote: > > Hi all, > > with the recent kernel 3.19, I get a kernel warning when I start my > KVM guest on s390 with virtio balloon enabled: > > [ 0.839687] do not call blocking ops when !TASK_RUNNING; state=1 set at > [<0000000000174a1e>] prepare_to_wait_event+0x7e/0x108 > [ 0.839694] ------------[ cut here ]------------ > [ 0.839697] WARNING: at kernel/sched/core.c:7326 > [ 0.839698] Modules linked in: > [ 0.839702] CPU: 0 PID: 46 Comm: vballoon Not tainted 3.19.0 #233 > [ 0.839705] task: 00000000021d0000 ti: 00000000021d8000 task.ti: 00000000021d8000 > [ 0.839707] Krnl PSW : 0704c00180000000 000000000015bf8e (__might_sleep+0x8e/0x98) > [ 0.839713] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 EA:3 > Krnl GPRS: 000000000000000d 00000000021d0000 0000000000000071 0000000000000001 > [ 0.839718] 0000000000675ace 0000000001998c50 cccccccccccccccc cccccccccccccccc > [ 0.839720] 0000000000982134 000000000058f824 0000000000a008a8 0000000000000000 > [ 0.839722] 00000000000004d9 00000000007ea992 000000000015bf8a 00000000021dbc28 > [ 0.839731] Krnl Code: 000000000015bf7e: c0200033e838 larl %r2,7d8fee > 000000000015bf84: c0e50028cd62 brasl %r14,675a48 > #000000000015bf8a: a7f40001 brc 15,15bf8c > >000000000015bf8e: 9201a000 mvi 0(%r10),1 > 000000000015bf92: a7f4ffe2 brc 15,15bf56 > 000000000015bf96: 0707 bcr 0,%r7 > 000000000015bf98: ebdff0800024 stmg %r13,%r15,128(%r15) > 000000000015bf9e: a7f13fe0 tmll %r15,16352 > [ 0.839749] Call Trace: > [ 0.839751] ([<000000000015bf8a>] __might_sleep+0x8a/0x98) > [ 0.839756] [<000000000028a562>] __kmalloc+0x272/0x350 > [ 0.839759] [<000000000058f824>] virtio_ccw_get_config+0x3c/0x100 > [ 0.839762] [<000000000049fcb0>] balloon+0x1b8/0x330 > [ 0.839765] [<00000000001529c8>] kthread+0x120/0x138 > [ 0.839767] [<0000000000683c22>] kernel_thread_starter+0x6/0xc > [ 0.839770] [<0000000000683c1c>] kernel_thread_starter+0x0/0xc > [ 0.839772] no locks held by vballoon/46. > [ 0.839773] Last Breaking-Event-Address: > [ 0.839776] [<000000000015bf8a>] __might_sleep+0x8a/0x98 > [ 0.839778] ---[ end trace d27fcdfa27273d7c ]--- > > The problem seems to be this code in balloon() in > drivers/virtio/virtio_balloon.c: > > wait_event_interruptible(vb->config_change, > (diff = towards_target(vb)) != 0 > || vb->need_stats_update > || kthread_should_stop() > || freezing(current)); > > wait_event_interruptible() sets the state of the current task to > TASK_INTERRUPTIBLE, then checks the condition. The condition contains > towards_target() which reads the virtio config space via virtio_cread(). > On s390, this then triggers virtio_ccw_get_config() - and this function > calls some other functions again that might sleep (e.g. kzalloc or > wait_event in ccw_io_helper) ... and this causes the new kernel warning > message with kernel 3.19. > > I think it would be quite difficult or at least ugly to rewrite > virtio_ccw_get_config() so that it does not call sleepable functions > anymore. Yes: The config-space interacting functions for virtio-ccw trigger channel I/O, which is by nature asynchronous. No way to get this non-sleeping without really ugly hacks. > So would it be feasible to rewrite the balloon() function that > it does not call the towards_target() in its wait_event condition > anymore? I am unfortunately not that familiar with the balloon code > semantics, so any help is very appreciated here! It might be possible to use nested wait event functions like wake_woken(), but I haven't looked into that deeply. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
