Messages in this thread |  | | Date | Thu, 9 Jul 2020 09:45:30 -0700 | From | "Paul E. McKenney" <> | Subject | Re: KASAN: stack-out-of-bounds Read in csd_lock_record |
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On Thu, Jul 09, 2020 at 12:13:44PM +0200, Dmitry Vyukov wrote: > On Tue, Jul 7, 2020 at 6:26 PM Paul E. McKenney <paulmck@kernel.org> wrote: > > > > On Tue, Jul 07, 2020 at 05:51:48PM +0200, Dmitry Vyukov wrote: > > > On Sat, Jul 4, 2020 at 8:34 PM Dmitry Vyukov <dvyukov@google.com> wrote: > > > > > > > > On Sat, Jul 4, 2020 at 6:45 PM Paul E. McKenney <paulmck@kernel.org> wrote: > > > > > > > > > > On Fri, Jul 03, 2020 at 04:31:22PM -0700, syzbot wrote: > > > > > > Hello, > > > > > > > > > > > > syzbot found the following crash on: > > > > > > > > > > > > HEAD commit: 9e50b94b Add linux-next specific files for 20200703 > > > > > > git tree: linux-next > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1024b405100000 > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=f99cc0faa1476ed6 > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=0f719294463916a3fc0e > > > > > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16dc490f100000 > > > > > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > > > Reported-by: syzbot+0f719294463916a3fc0e@syzkaller.appspotmail.com > > > > > > > > > > Good catch! A call to csd_lock_record() was on the wrong side of a > > > > > call to csd_unlock(). > > > > > > > > Thanks for taking a look. > > > > > > > > > But is folded into another commit for bisectability reasons, so > > > > > "Reported-by" would not make sense. I have instead added this to the > > > > > commit log: > > > > > > > > > > [ paulmck: Fix for syzbot+0f719294463916a3fc0e@syzkaller.appspotmail.com ] > > > > > Link: https://lore.kernel.org/lkml/00000000000042f21905a991ecea@google.com > > > > > Link: https://lore.kernel.org/lkml/0000000000002ef21705a9933cf3@google.com > > > > > > > > This should work, as far as I remember sybot looks for the email+hash > > > > anywhere in the commit. > > > > FWIW Tested-by can make sense as well. > > > > > > Paul, there is also some spike of stalls in smp_call_function, > > > if you look at the top ones at: > > > https://syzkaller.appspot.com/upstream#open > > > > > > Can these be caused by the same root cause? > > > I am not sure what trees the bug was/is present... This seems to only > > > happen on linux-next and nowhere else. But these stalls equally happen > > > on mainline... > > > > I would be surprised, given that the csd_unlock() was before the faulting > > reference. But then again, I have been surprised before. > > Yes, it seems unrelated. > It looks like something broken in the kernel recently and now instead > of diagnosing a stall on one CPU, it diagnoses it as a stall in > smp_call_function on another CPU. This produces large number of > assorted stall reports which are not too actionable... > > > > You aren't running scftorture with its longwait parameter set to a > > non-zero value, are you? In that case, stalls are expected behavior. > > This is to support test the CSD lock diagnostics in -rcu. Which isn't > > in mainline yet, so maybe I am asking a stupid question. > > Since I don't know what is scftorture/longwait, I guess I am not running it :) > > > If these are repeatable, one thing to try is to build the kernel with > > CSD_LOCK_WAIT_DEBUG=y. This requires c6c67d89c059 ("smp: Add source and > > destination CPUs to __call_single_data") and 216d15e0d870 ("kernel/smp: > > Provide CSD lock timeout diagnostics") from the -rcu tree's "dev" branch. > > This will dump out the smp_call_function() function that was to be > > invoked, on the off-chance that the problem is something like lock > > contention in that function. > > Here are some with reproducers: > https://syzkaller.appspot.com/bug?id=8a1e95291152ce5afea43c103a1fd62a257fcf4b > https://syzkaller.appspot.com/bug?id=5e3ac329b6304aacc6304cfaab1a514bca12ce82 > https://syzkaller.appspot.com/bug?id=a01b4478f89e19cee91531f7c2b7751f0caf8c0c > https://syzkaller.appspot.com/bug?id=e4caef9fc41d0c019c532a4257faec129699a42e > > But the question is if this CSD_LOCK_WAIT_DEBUG=y is useful in > general? Should we enable it all the time?
The CSD_LOCK_WAIT_DEBUG functionality is quite new, so it is quite possible that it is causing rather than detecting problems. ;-)
But once it is stable, then yes, it might be quite generally useful.
Thanx, Paul
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