On Tue, 16 Nov 2010 12:41:17 -0800 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 16 Nov 2010 19:17:48 +0900 > Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote: > > > From: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> > > > > __mem_cgroup_try_charge() can be called under down_write(&mmap_sem)(e.g. > > mlock does it). This means it can cause deadlock if it races with move charge: > > > > Ex.1) > > move charge | try charge > > --------------------------------------+------------------------------ > > mem_cgroup_can_attach() | down_write(&mmap_sem) > > mc.moving_task = current | .. > > mem_cgroup_precharge_mc() | __mem_cgroup_try_charge() > > mem_cgroup_count_precharge() | prepare_to_wait() > > down_read(&mmap_sem) | if (mc.moving_task) > > -> cannot aquire the lock | -> true > > | schedule() > > > > Ex.2) > > move charge | try charge > > --------------------------------------+------------------------------ > > mem_cgroup_can_attach() | > > mc.moving_task = current | > > mem_cgroup_precharge_mc() | > > mem_cgroup_count_precharge() | > > down_read(&mmap_sem) | > > .. | > > up_read(&mmap_sem) | > > | down_write(&mmap_sem) > > mem_cgroup_move_task() | .. > > mem_cgroup_move_charge() | __mem_cgroup_try_charge() > > down_read(&mmap_sem) | prepare_to_wait() > > -> cannot aquire the lock | if (mc.moving_task) > > | -> true > > | schedule() > > > > To avoid this deadlock, we do all the move charge works (both can_attach() and > > attach()) under one mmap_sem section. > > And after this patch, we set/clear mc.moving_task outside mc.lock, because we > > use the lock only to check mc.from/to. > > > > Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> > > I put this in the send-to-Linus-in-about-a-week queue. > > > Cc: <stable@xxxxxxxxxx> > > The patch doesn't apply well to 2.6.36 so if we do want it backported > then please prepare a tested backport for the -stable guys? > O.K. I'll test a backported patch for 2.6.36.y and send it after this is merged into mainline. Thanks, Daisuke Nishimura. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>