On Thu, 2014-04-24 at 10:32 -0400, Tejun Heo wrote: > Hello, > > On Thu, Apr 24, 2014 at 04:37:23PM +0800, Li Zhong wrote: > > On Wed, 2014-04-23 at 10:39 -0400, Tejun Heo wrote: > > After thinking it harder, I still couldn't see ABBA here ... > > > > the active protection taken here is for "probe/release" which will not > > be waited for removing something like "online" under cpu#? Or my > > assumption that s_active for different files are different locks are > > completely wrong? Or I missed something else? > > I'm probably confused about the locking. I was thinking a scenario > like the following. > > A. CPU on/offline > > grabs s_active protection of online node > grabs cpu subsys mutex > perform on/offline > releases cpu subsys mutex > releases s_active protection of online node
so the chain here is s_active(online) -> cpu_subsys_mutex > > B. CPU release > > grabs s_active protection of release node > grabs cpu subsys mutex > performs removal of the CPU > removes the online node > releases cpu subsys mutex > releases s_active protection of release node and the chain here is s_active(release) -> cpu_subsys_mutex -> s_active(online) > > A nests cpu subsys mutex under s_active of the online node. B nests > s_active of the online node under the cpu subsys mutex. What am I > missing? >From the above two chain, I think the problem is cpu_subsys_mutex and s_active(online), which is the deadlock we are trying to solve in patch #2. I seems to me s_active(release) here doesn't have lock issues? Thanks, Zhong > > Thanks. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
