[BUG] Circular locking dependency - DRM/CMA/MM/hotplug/... (original) (raw)

Daniel Vetter daniel at ffwll.ch
Wed Feb 12 10:29:01 PST 2014

On Wed, Feb 12, 2014 at 04:33:17PM +0000, Russell King - ARM Linux wrote:

On Wed, Feb 12, 2014 at 04:40:50PM +0100, Marek Szyprowski wrote: >> -> #3 (consolelock){+.+.+.}: _>> [] lockacquire+0x151c/0x1ca0 >> [] lockacquire+0xa0/0x130 >> [] consolelock+0x60/0x74 >> [] consolecpunotify+0x28/0x34 >> [] notifiercallchain+0x4c/0x8c _>> [] rawnotifiercallchain+0x1c/0x24 _>> [] cpunotify+0x34/0x50 >> [] cpunotifynofail+0x18/0x24 >> [] cpudown+0x100/0x244 >> [] cpudown+0x30/0x44 >> [] cpusubsysoffline+0x14/0x18 >> [] deviceoffline+0x94/0xbc >> [] onlinestore+0x4c/0x74 >> [] devattrstore+0x20/0x2c >> [] sysfskfwrite+0x54/0x58 >> [] kernfsfopwrite+0xc4/0x160 >> [] vfswrite+0xbc/0x184 >> [] SySwrite+0x48/0x70 >> [] retfastsyscall+0x0/0x48

cpudown() takes cpuhotplug.lock, so here we have: cpuhotplug.lock consolelock

The patche I've linked in my other mail will break the chain here, so should solve this. And apparently with cpu hotplug we can hit this, too. And having banged my head against the console_lock wall I think doing a trylock here is generally the sanest option.

So imo we can just blame console_lock, not need to either beat up v4l, drm, cma or anyone else really ;-)

Cheers, Daniel

Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch

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