From: "Michael S. Tsirkin" <mst@redhat.com> To: "Paul E. McKenney" <paulmck@linux.ibm.com> Cc: Joel Fernandes <joel@joelfernandes.org>, Matthew Wilcox <willy@infradead.org>, aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jasowang@redhat.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Date: Mon, 22 Jul 2019 12:13:40 -0400 [thread overview] Message-ID: <20190722120011-mutt-send-email-mst@kernel.org> (raw) In-Reply-To: <20190722155534.GG14271@linux.ibm.com> On Mon, Jul 22, 2019 at 08:55:34AM -0700, Paul E. McKenney wrote: > On Mon, Jul 22, 2019 at 11:47:24AM -0400, Michael S. Tsirkin wrote: > > On Mon, Jul 22, 2019 at 11:14:39AM -0400, Joel Fernandes wrote: > > > [snip] > > > > > Would it make sense to have call_rcu() check to see if there are many > > > > > outstanding requests on this CPU and if so process them before returning? > > > > > That would ensure that frequent callers usually ended up doing their > > > > > own processing. > > > > > > Other than what Paul already mentioned about deadlocks, I am not sure if this > > > would even work for all cases since call_rcu() has to wait for a grace > > > period. > > > > > > So, if the number of outstanding requests are higher than a certain amount, > > > then you *still* have to wait for some RCU configurations for the grace > > > period duration and cannot just execute the callback in-line. Did I miss > > > something? > > > > > > Can waiting in-line for a grace period duration be tolerated in the vhost case? > > > > > > thanks, > > > > > > - Joel > > > > No, but it has many other ways to recover (try again later, drop a > > packet, use a slower copy to/from user). > > True enough! And your idea of taking recovery action based on the number > of callbacks seems like a good one while we are getting RCU's callback > scheduling improved. > > By the way, was this a real problem that you could make happen on real > hardware? > If not, I would suggest just letting RCU get improved over > the next couple of releases. So basically use kfree_rcu but add a comment saying e.g. "WARNING: in the future callers of kfree_rcu might need to check that not too many callbacks get queued. In that case, we can disable the optimization, or recover in some other way. Watch this space." > If it is something that you actually made happen, please let me know > what (if anything) you need from me for your callback-counting EBUSY > scheme. > > Thanx, Paul If you mean kfree_rcu causing OOM then no, it's all theoretical. If you mean synchronize_rcu stalling to the point where guest will OOPs, then yes, that's not too hard to trigger.
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com> To: "Paul E. McKenney" <paulmck@linux.ibm.com> Cc: mhocko@suse.com, peterz@infradead.org, jasowang@redhat.com, ldv@altlinux.org, james.bottomley@hansenpartnership.com, linux-mm@kvack.org, namit@vmware.com, Joel Fernandes <joel@joelfernandes.org>, mingo@kernel.org, elena.reshetova@intel.com, aarcange@redhat.com, davem@davemloft.net, Matthew Wilcox <willy@infradead.org>, hch@infradead.org, linux-arm-kernel@lists.infradead.org, keescook@chromium.org, syzkaller-bugs@googlegroups.com, jglisse@redhat.com, viro@zeniv.linux.org.uk, christian@brauner.io, wad@chromium.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, luto@amacapital.net, ebiederm@xmission.com, akpm@linux-foundation.org, guro@fb.com Subject: Re: RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Date: Mon, 22 Jul 2019 12:13:40 -0400 [thread overview] Message-ID: <20190722120011-mutt-send-email-mst@kernel.org> (raw) In-Reply-To: <20190722155534.GG14271@linux.ibm.com> On Mon, Jul 22, 2019 at 08:55:34AM -0700, Paul E. McKenney wrote: > On Mon, Jul 22, 2019 at 11:47:24AM -0400, Michael S. Tsirkin wrote: > > On Mon, Jul 22, 2019 at 11:14:39AM -0400, Joel Fernandes wrote: > > > [snip] > > > > > Would it make sense to have call_rcu() check to see if there are many > > > > > outstanding requests on this CPU and if so process them before returning? > > > > > That would ensure that frequent callers usually ended up doing their > > > > > own processing. > > > > > > Other than what Paul already mentioned about deadlocks, I am not sure if this > > > would even work for all cases since call_rcu() has to wait for a grace > > > period. > > > > > > So, if the number of outstanding requests are higher than a certain amount, > > > then you *still* have to wait for some RCU configurations for the grace > > > period duration and cannot just execute the callback in-line. Did I miss > > > something? > > > > > > Can waiting in-line for a grace period duration be tolerated in the vhost case? > > > > > > thanks, > > > > > > - Joel > > > > No, but it has many other ways to recover (try again later, drop a > > packet, use a slower copy to/from user). > > True enough! And your idea of taking recovery action based on the number > of callbacks seems like a good one while we are getting RCU's callback > scheduling improved. > > By the way, was this a real problem that you could make happen on real > hardware? > If not, I would suggest just letting RCU get improved over > the next couple of releases. So basically use kfree_rcu but add a comment saying e.g. "WARNING: in the future callers of kfree_rcu might need to check that not too many callbacks get queued. In that case, we can disable the optimization, or recover in some other way. Watch this space." > If it is something that you actually made happen, please let me know > what (if anything) you need from me for your callback-counting EBUSY > scheme. > > Thanx, Paul If you mean kfree_rcu causing OOM then no, it's all theoretical. If you mean synchronize_rcu stalling to the point where guest will OOPs, then yes, that's not too hard to trigger. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-07-22 16:13 UTC|newest] Thread overview: 176+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-19 3:35 WARNING in __mmdrop syzbot 2019-07-20 10:08 ` syzbot 2019-07-20 10:08 ` syzbot 2019-07-20 10:08 ` syzbot 2019-07-21 10:02 ` Michael S. Tsirkin 2019-07-21 10:02 ` Michael S. Tsirkin 2019-07-21 12:18 ` Michael S. Tsirkin 2019-07-21 12:18 ` Michael S. Tsirkin 2019-07-22 5:24 ` Jason Wang 2019-07-22 5:24 ` Jason Wang 2019-07-22 8:08 ` Michael S. Tsirkin 2019-07-22 8:08 ` Michael S. Tsirkin 2019-07-23 4:01 ` Jason Wang 2019-07-23 4:01 ` Jason Wang 2019-07-23 5:01 ` Michael S. Tsirkin 2019-07-23 5:01 ` Michael S. Tsirkin 2019-07-23 5:47 ` Jason Wang 2019-07-23 5:47 ` Jason Wang 2019-07-23 7:23 ` Michael S. Tsirkin 2019-07-23 7:23 ` Michael S. Tsirkin 2019-07-23 7:53 ` Jason Wang 2019-07-23 7:53 ` Jason Wang 2019-07-23 8:10 ` Michael S. Tsirkin 2019-07-23 8:10 ` Michael S. Tsirkin 2019-07-23 8:49 ` Jason Wang 2019-07-23 8:49 ` Jason Wang 2019-07-23 9:26 ` Michael S. Tsirkin 2019-07-23 9:26 ` Michael S. Tsirkin 2019-07-23 13:31 ` Jason Wang 2019-07-23 13:31 ` Jason Wang 2019-07-25 5:52 ` Michael S. Tsirkin 2019-07-25 5:52 ` Michael S. Tsirkin 2019-07-25 7:43 ` Jason Wang 2019-07-25 7:43 ` Jason Wang 2019-07-25 8:28 ` Michael S. Tsirkin 2019-07-25 8:28 ` Michael S. Tsirkin 2019-07-25 13:21 ` Jason Wang 2019-07-25 13:21 ` Jason Wang 2019-07-25 13:26 ` Michael S. Tsirkin 2019-07-25 13:26 ` Michael S. Tsirkin 2019-07-25 14:25 ` Jason Wang 2019-07-25 14:25 ` Jason Wang 2019-07-26 11:49 ` Michael S. Tsirkin 2019-07-26 11:49 ` Michael S. Tsirkin 2019-07-26 12:00 ` Jason Wang 2019-07-26 12:00 ` Jason Wang 2019-07-26 12:38 ` Michael S. Tsirkin 2019-07-26 12:38 ` Michael S. Tsirkin 2019-07-26 12:53 ` Jason Wang 2019-07-26 12:53 ` Jason Wang 2019-07-26 13:36 ` Jason Wang 2019-07-26 13:36 ` Jason Wang 2019-07-26 13:49 ` Michael S. Tsirkin 2019-07-26 13:49 ` Michael S. Tsirkin 2019-07-29 5:54 ` Jason Wang 2019-07-29 5:54 ` Jason Wang 2019-07-29 8:59 ` Michael S. Tsirkin 2019-07-29 8:59 ` Michael S. Tsirkin 2019-07-29 14:24 ` Jason Wang 2019-07-29 14:24 ` Jason Wang 2019-07-29 14:44 ` Michael S. Tsirkin 2019-07-29 14:44 ` Michael S. Tsirkin 2019-07-30 7:44 ` Jason Wang 2019-07-30 7:44 ` Jason Wang 2019-07-30 8:03 ` Jason Wang 2019-07-30 8:03 ` Jason Wang 2019-07-30 15:08 ` Michael S. Tsirkin 2019-07-30 15:08 ` Michael S. Tsirkin 2019-07-31 8:49 ` Jason Wang 2019-07-31 8:49 ` Jason Wang 2019-07-31 23:00 ` Jason Gunthorpe 2019-07-31 23:00 ` Jason Gunthorpe 2019-07-26 13:47 ` Michael S. Tsirkin 2019-07-26 13:47 ` Michael S. Tsirkin 2019-07-26 14:00 ` Jason Wang 2019-07-26 14:00 ` Jason Wang 2019-07-26 14:10 ` Michael S. Tsirkin 2019-07-26 14:10 ` Michael S. Tsirkin 2019-07-26 15:03 ` Jason Gunthorpe 2019-07-26 15:03 ` Jason Gunthorpe 2019-07-29 5:56 ` Jason Wang 2019-07-29 5:56 ` Jason Wang 2019-07-21 12:28 ` RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Michael S. Tsirkin 2019-07-21 12:28 ` Michael S. Tsirkin 2019-07-21 13:17 ` Paul E. McKenney 2019-07-21 13:17 ` Paul E. McKenney 2019-07-21 17:53 ` Michael S. Tsirkin 2019-07-21 17:53 ` Michael S. Tsirkin 2019-07-21 19:28 ` Paul E. McKenney 2019-07-21 19:28 ` Paul E. McKenney 2019-07-22 7:56 ` Michael S. Tsirkin 2019-07-22 7:56 ` Michael S. Tsirkin 2019-07-22 11:57 ` Paul E. McKenney 2019-07-22 11:57 ` Paul E. McKenney 2019-07-21 21:08 ` Matthew Wilcox 2019-07-21 21:08 ` Matthew Wilcox 2019-07-21 23:31 ` Paul E. McKenney 2019-07-21 23:31 ` Paul E. McKenney 2019-07-22 7:52 ` Michael S. Tsirkin 2019-07-22 7:52 ` Michael S. Tsirkin 2019-07-22 11:51 ` Paul E. McKenney 2019-07-22 11:51 ` Paul E. McKenney 2019-07-22 13:41 ` Jason Gunthorpe 2019-07-22 13:41 ` Jason Gunthorpe 2019-07-22 15:52 ` Paul E. McKenney 2019-07-22 15:52 ` Paul E. McKenney 2019-07-22 16:04 ` Jason Gunthorpe 2019-07-22 16:04 ` Jason Gunthorpe 2019-07-22 16:15 ` Michael S. Tsirkin 2019-07-22 16:15 ` Michael S. Tsirkin 2019-07-22 16:15 ` Paul E. McKenney 2019-07-22 16:15 ` Paul E. McKenney 2019-07-22 15:14 ` Joel Fernandes 2019-07-22 15:14 ` Joel Fernandes 2019-07-22 15:47 ` Michael S. Tsirkin 2019-07-22 15:47 ` Michael S. Tsirkin 2019-07-22 15:55 ` Paul E. McKenney 2019-07-22 15:55 ` Paul E. McKenney 2019-07-22 16:13 ` Michael S. Tsirkin [this message] 2019-07-22 16:13 ` Michael S. Tsirkin 2019-07-22 16:25 ` Paul E. McKenney 2019-07-22 16:25 ` Paul E. McKenney 2019-07-22 16:32 ` Michael S. Tsirkin 2019-07-22 16:32 ` Michael S. Tsirkin 2019-07-22 18:58 ` Paul E. McKenney 2019-07-22 18:58 ` Paul E. McKenney 2019-07-22 5:21 ` WARNING in __mmdrop Jason Wang 2019-07-22 5:21 ` Jason Wang 2019-07-22 8:02 ` Michael S. Tsirkin 2019-07-22 8:02 ` Michael S. Tsirkin 2019-07-23 3:55 ` Jason Wang 2019-07-23 3:55 ` Jason Wang 2019-07-23 5:02 ` Michael S. Tsirkin 2019-07-23 5:02 ` Michael S. Tsirkin 2019-07-23 5:48 ` Jason Wang 2019-07-23 5:48 ` Jason Wang 2019-07-23 7:25 ` Michael S. Tsirkin 2019-07-23 7:25 ` Michael S. Tsirkin 2019-07-23 7:55 ` Jason Wang 2019-07-23 7:55 ` Jason Wang 2019-07-23 7:56 ` Michael S. Tsirkin 2019-07-23 7:56 ` Michael S. Tsirkin 2019-07-23 8:42 ` Jason Wang 2019-07-23 8:42 ` Jason Wang 2019-07-23 10:27 ` Michael S. Tsirkin 2019-07-23 10:27 ` Michael S. Tsirkin 2019-07-23 13:34 ` Jason Wang 2019-07-23 13:34 ` Jason Wang 2019-07-23 15:02 ` Michael S. Tsirkin 2019-07-23 15:02 ` Michael S. Tsirkin 2019-07-24 2:17 ` Jason Wang 2019-07-24 2:17 ` Jason Wang 2019-07-24 8:05 ` Michael S. Tsirkin 2019-07-24 8:05 ` Michael S. Tsirkin 2019-07-24 10:08 ` Jason Wang 2019-07-24 10:08 ` Jason Wang 2019-07-24 18:25 ` Michael S. Tsirkin 2019-07-24 18:25 ` Michael S. Tsirkin 2019-07-25 3:44 ` Jason Wang 2019-07-25 3:44 ` Jason Wang 2019-07-25 5:09 ` Michael S. Tsirkin 2019-07-25 5:09 ` Michael S. Tsirkin 2019-07-24 16:53 ` Jason Gunthorpe 2019-07-24 16:53 ` Jason Gunthorpe 2019-07-24 18:25 ` Michael S. Tsirkin 2019-07-24 18:25 ` Michael S. Tsirkin 2019-07-23 10:42 ` Michael S. Tsirkin 2019-07-23 10:42 ` Michael S. Tsirkin 2019-07-23 13:37 ` Jason Wang 2019-07-23 13:37 ` Jason Wang 2019-07-22 14:11 ` Jason Gunthorpe 2019-07-22 14:11 ` Jason Gunthorpe 2019-07-25 6:02 ` Michael S. Tsirkin 2019-07-25 6:02 ` Michael S. Tsirkin 2019-07-25 7:44 ` Jason Wang 2019-07-25 7:44 ` Jason Wang
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20190722120011-mutt-send-email-mst@kernel.org \ --to=mst@redhat.com \ --cc=aarcange@redhat.com \ --cc=akpm@linux-foundation.org \ --cc=christian@brauner.io \ --cc=davem@davemloft.net \ --cc=ebiederm@xmission.com \ --cc=elena.reshetova@intel.com \ --cc=guro@fb.com \ --cc=hch@infradead.org \ --cc=james.bottomley@hansenpartnership.com \ --cc=jasowang@redhat.com \ --cc=jglisse@redhat.com \ --cc=joel@joelfernandes.org \ --cc=keescook@chromium.org \ --cc=ldv@altlinux.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-mm@kvack.org \ --cc=linux-parisc@vger.kernel.org \ --cc=luto@amacapital.net \ --cc=mhocko@suse.com \ --cc=mingo@kernel.org \ --cc=namit@vmware.com \ --cc=paulmck@linux.ibm.com \ --cc=peterz@infradead.org \ --cc=syzkaller-bugs@googlegroups.com \ --cc=viro@zeniv.linux.org.uk \ --cc=wad@chromium.org \ --cc=willy@infradead.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.