* Re: rcu_preempt detected stalls. [not found] ` <20141027211329.GJ5718@linux.vnet.ibm.com> @ 2014-10-27 23:44 ` Paul E. McKenney 2014-11-13 23:07 ` Paul E. McKenney 0 siblings, 1 reply; 3+ messages in thread From: Paul E. McKenney @ 2014-10-27 23:44 UTC (permalink / raw) To: Sasha Levin; +Cc: Dave Jones, Linux Kernel, htejun, linux-mm On Mon, Oct 27, 2014 at 02:13:29PM -0700, Paul E. McKenney wrote: > On Fri, Oct 24, 2014 at 12:39:15PM -0400, Sasha Levin wrote: > > On 10/24/2014 12:13 PM, Paul E. McKenney wrote: > > > On Fri, Oct 24, 2014 at 08:28:40AM -0400, Sasha Levin wrote: > > >> > On 10/23/2014 03:58 PM, Paul E. McKenney wrote: > > >>> > > On Thu, Oct 23, 2014 at 02:55:43PM -0400, Sasha Levin wrote: > > >>>>> > >> > On 10/23/2014 02:39 PM, Paul E. McKenney wrote: > > >>>>>>> > >>> > > On Tue, Oct 14, 2014 at 10:35:10PM -0400, Sasha Levin wrote: > > >>>>>>>>> > >>>> > >> On 10/13/2014 01:35 PM, Dave Jones wrote: > > >>>>>>>>>>> > >>>>> > >>> oday in "rcu stall while fuzzing" news: > > >>>>>>>>>>> > >>>>> > >>> > > >>>>>>>>>>> > >>>>> > >>> INFO: rcu_preempt detected stalls on CPUs/tasks: > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > >>>>>>>>>>> > >>>>> > >>> (detected by 0, t=6502 jiffies, g=75434, c=75433, q=0) > > >>>>>>>>> > >>>> > >> > > >>>>>>>>> > >>>> > >> I've complained about RCU stalls couple days ago (in a different context) > > >>>>>>>>> > >>>> > >> on -next. I guess whatever causing them made it into Linus's tree? > > >>>>>>>>> > >>>> > >> > > >>>>>>>>> > >>>> > >> https://lkml.org/lkml/2014/10/11/64 > > >>>>>>> > >>> > > > > >>>>>>> > >>> > > And on that one, I must confess that I don't see where the RCU read-side > > >>>>>>> > >>> > > critical section might be. > > >>>>>>> > >>> > > > > >>>>>>> > >>> > > Hmmm... Maybe someone forgot to put an rcu_read_unlock() somewhere. > > >>>>>>> > >>> > > Can you reproduce this with CONFIG_PROVE_RCU=y? > > >>>>> > >> > > > >>>>> > >> > Paul, if that was directed to me - Yes, I see stalls with CONFIG_PROVE_RCU > > >>>>> > >> > set and nothing else is showing up before/after that. > > >>> > > Indeed it was directed to you. ;-) > > >>> > > > > >>> > > Does the following crude diagnostic patch turn up anything? > > >> > > > >> > Nope, seeing stalls but not seeing that pr_err() you added. > > > OK, color me confused. Could you please send me the full dmesg or a > > > pointer to it? > > > > Attached. > > Thank you! I would complain about the FAULT_INJECTION messages, but > they don't appear to be happening all that frequently. > > The stack dumps do look different here. I suspect that this is a real > issue in the VM code. And to that end... The filemap_map_pages() function does have loop over a list of pages. I wonder if the rcu_read_lock() should be moved into the radix_tree_for_each_slot() loop. CCing linux-mm for their thoughts, though it looks to me like the current radix_tree_for_each_slot() wants to be under RCU protection. But I am not seeing anything that requires all iterations of the loop to be under the same RCU read-side critical section. Maybe something like the following patch? Thanx, Paul ------------------------------------------------------------------------ mm: Attempted fix for RCU CPU stall warning It appears that filemap_map_pages() can stay in a single RCU read-side critical section for a very long time if given a large area to map. This could result in RCU CPU stall warnings. This commit therefore breaks the read-side critical section into per-iteration critical sections, taking care to make sure that the radix_tree_for_each_slot() call itself remains in an RCU read-side critical section, as required. Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> diff --git a/mm/filemap.c b/mm/filemap.c index 14b4642279f1..f78f144fb41f 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2055,6 +2055,8 @@ skip: next: if (iter.index == vmf->max_pgoff) break; + rcu_read_unlock(); + rcu_read_lock(); } rcu_read_unlock(); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: rcu_preempt detected stalls. 2014-10-27 23:44 ` rcu_preempt detected stalls Paul E. McKenney @ 2014-11-13 23:07 ` Paul E. McKenney 2014-11-13 23:10 ` Sasha Levin 0 siblings, 1 reply; 3+ messages in thread From: Paul E. McKenney @ 2014-11-13 23:07 UTC (permalink / raw) To: Sasha Levin; +Cc: Dave Jones, Linux Kernel, htejun, linux-mm On Mon, Oct 27, 2014 at 04:44:25PM -0700, Paul E. McKenney wrote: > On Mon, Oct 27, 2014 at 02:13:29PM -0700, Paul E. McKenney wrote: > > On Fri, Oct 24, 2014 at 12:39:15PM -0400, Sasha Levin wrote: > > > On 10/24/2014 12:13 PM, Paul E. McKenney wrote: > > > > On Fri, Oct 24, 2014 at 08:28:40AM -0400, Sasha Levin wrote: > > > >> > On 10/23/2014 03:58 PM, Paul E. McKenney wrote: > > > >>> > > On Thu, Oct 23, 2014 at 02:55:43PM -0400, Sasha Levin wrote: > > > >>>>> > >> > On 10/23/2014 02:39 PM, Paul E. McKenney wrote: > > > >>>>>>> > >>> > > On Tue, Oct 14, 2014 at 10:35:10PM -0400, Sasha Levin wrote: > > > >>>>>>>>> > >>>> > >> On 10/13/2014 01:35 PM, Dave Jones wrote: > > > >>>>>>>>>>> > >>>>> > >>> oday in "rcu stall while fuzzing" news: > > > >>>>>>>>>>> > >>>>> > >>> > > > >>>>>>>>>>> > >>>>> > >>> INFO: rcu_preempt detected stalls on CPUs/tasks: > > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > > >>>>>>>>>>> > >>>>> > >>> (detected by 0, t=6502 jiffies, g=75434, c=75433, q=0) > > > >>>>>>>>> > >>>> > >> > > > >>>>>>>>> > >>>> > >> I've complained about RCU stalls couple days ago (in a different context) > > > >>>>>>>>> > >>>> > >> on -next. I guess whatever causing them made it into Linus's tree? > > > >>>>>>>>> > >>>> > >> > > > >>>>>>>>> > >>>> > >> https://lkml.org/lkml/2014/10/11/64 > > > >>>>>>> > >>> > > > > > >>>>>>> > >>> > > And on that one, I must confess that I don't see where the RCU read-side > > > >>>>>>> > >>> > > critical section might be. > > > >>>>>>> > >>> > > > > > >>>>>>> > >>> > > Hmmm... Maybe someone forgot to put an rcu_read_unlock() somewhere. > > > >>>>>>> > >>> > > Can you reproduce this with CONFIG_PROVE_RCU=y? > > > >>>>> > >> > > > > >>>>> > >> > Paul, if that was directed to me - Yes, I see stalls with CONFIG_PROVE_RCU > > > >>>>> > >> > set and nothing else is showing up before/after that. > > > >>> > > Indeed it was directed to you. ;-) > > > >>> > > > > > >>> > > Does the following crude diagnostic patch turn up anything? > > > >> > > > > >> > Nope, seeing stalls but not seeing that pr_err() you added. > > > > OK, color me confused. Could you please send me the full dmesg or a > > > > pointer to it? > > > > > > Attached. > > > > Thank you! I would complain about the FAULT_INJECTION messages, but > > they don't appear to be happening all that frequently. > > > > The stack dumps do look different here. I suspect that this is a real > > issue in the VM code. > > And to that end... The filemap_map_pages() function does have loop over > a list of pages. I wonder if the rcu_read_lock() should be moved into > the radix_tree_for_each_slot() loop. CCing linux-mm for their thoughts, > though it looks to me like the current radix_tree_for_each_slot() wants > to be under RCU protection. But I am not seeing anything that requires > all iterations of the loop to be under the same RCU read-side critical > section. Maybe something like the following patch? Just following up, did the patch below help? Thanx, Paul > ------------------------------------------------------------------------ > > mm: Attempted fix for RCU CPU stall warning > > It appears that filemap_map_pages() can stay in a single RCU read-side > critical section for a very long time if given a large area to map. > This could result in RCU CPU stall warnings. This commit therefore breaks > the read-side critical section into per-iteration critical sections, taking > care to make sure that the radix_tree_for_each_slot() call itself remains > in an RCU read-side critical section, as required. > > Reported-by: Sasha Levin <sasha.levin@oracle.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > diff --git a/mm/filemap.c b/mm/filemap.c > index 14b4642279f1..f78f144fb41f 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2055,6 +2055,8 @@ skip: > next: > if (iter.index == vmf->max_pgoff) > break; > + rcu_read_unlock(); > + rcu_read_lock(); > } > rcu_read_unlock(); > } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: rcu_preempt detected stalls. 2014-11-13 23:07 ` Paul E. McKenney @ 2014-11-13 23:10 ` Sasha Levin 0 siblings, 0 replies; 3+ messages in thread From: Sasha Levin @ 2014-11-13 23:10 UTC (permalink / raw) To: paulmck; +Cc: Dave Jones, Linux Kernel, htejun, linux-mm On 11/13/2014 06:07 PM, Paul E. McKenney wrote: > On Mon, Oct 27, 2014 at 04:44:25PM -0700, Paul E. McKenney wrote: >> > On Mon, Oct 27, 2014 at 02:13:29PM -0700, Paul E. McKenney wrote: >>> > > On Fri, Oct 24, 2014 at 12:39:15PM -0400, Sasha Levin wrote: >>>> > > > On 10/24/2014 12:13 PM, Paul E. McKenney wrote: >>>>> > > > > On Fri, Oct 24, 2014 at 08:28:40AM -0400, Sasha Levin wrote: >>>>>>> > > > >> > On 10/23/2014 03:58 PM, Paul E. McKenney wrote: >>>>>>>>> > > > >>> > > On Thu, Oct 23, 2014 at 02:55:43PM -0400, Sasha Levin wrote: >>>>>>>>>>>>> > > > >>>>> > >> > On 10/23/2014 02:39 PM, Paul E. McKenney wrote: >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > On Tue, Oct 14, 2014 at 10:35:10PM -0400, Sasha Levin wrote: >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> On 10/13/2014 01:35 PM, Dave Jones wrote: >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> oday in "rcu stall while fuzzing" news: >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> INFO: rcu_preempt detected stalls on CPUs/tasks: >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 >>>>>>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>>>> > >>>>> > >>> (detected by 0, t=6502 jiffies, g=75434, c=75433, q=0) >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> I've complained about RCU stalls couple days ago (in a different context) >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> on -next. I guess whatever causing them made it into Linus's tree? >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> >>>>>>>>>>>>>>>>>>>>> > > > >>>>>>>>> > >>>> > >> https://lkml.org/lkml/2014/10/11/64 >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > And on that one, I must confess that I don't see where the RCU read-side >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > critical section might be. >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > Hmmm... Maybe someone forgot to put an rcu_read_unlock() somewhere. >>>>>>>>>>>>>>>>> > > > >>>>>>> > >>> > > Can you reproduce this with CONFIG_PROVE_RCU=y? >>>>>>>>>>>>> > > > >>>>> > >> > >>>>>>>>>>>>> > > > >>>>> > >> > Paul, if that was directed to me - Yes, I see stalls with CONFIG_PROVE_RCU >>>>>>>>>>>>> > > > >>>>> > >> > set and nothing else is showing up before/after that. >>>>>>>>> > > > >>> > > Indeed it was directed to you. ;-) >>>>>>>>> > > > >>> > > >>>>>>>>> > > > >>> > > Does the following crude diagnostic patch turn up anything? >>>>>>> > > > >> > >>>>>>> > > > >> > Nope, seeing stalls but not seeing that pr_err() you added. >>>>> > > > > OK, color me confused. Could you please send me the full dmesg or a >>>>> > > > > pointer to it? >>>> > > > >>>> > > > Attached. >>> > > >>> > > Thank you! I would complain about the FAULT_INJECTION messages, but >>> > > they don't appear to be happening all that frequently. >>> > > >>> > > The stack dumps do look different here. I suspect that this is a real >>> > > issue in the VM code. >> > >> > And to that end... The filemap_map_pages() function does have loop over >> > a list of pages. I wonder if the rcu_read_lock() should be moved into >> > the radix_tree_for_each_slot() loop. CCing linux-mm for their thoughts, >> > though it looks to me like the current radix_tree_for_each_slot() wants >> > to be under RCU protection. But I am not seeing anything that requires >> > all iterations of the loop to be under the same RCU read-side critical >> > section. Maybe something like the following patch? > Just following up, did the patch below help? I'm not seeing any more stalls with filemap in them, but I don see different traces. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-10-27 23:44 ` rcu_preempt detected stalls Paul E. McKenney
2014-11-13 23:07 ` Paul E. McKenney
2014-11-13 23:10 ` Sasha Levin
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