Messages in this thread | | | Subject | Re: [locks] 6d390e4b5d: will-it-scale.per_process_ops -96.6% regression | From | yangerkun <> | Date | Tue, 17 Mar 2020 22:05:09 +0800 |
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On 2020/3/17 9:41, yangerkun wrote: > > > On 2020/3/17 1:26, Linus Torvalds wrote: >> On Mon, Mar 16, 2020 at 4:07 AM Jeff Layton <jlayton@kernel.org> wrote: >>> >>> >>> + /* >>> + * If fl_blocker is NULL, it won't be set again as this >>> thread "owns" >>> + * the lock and is the only one that might try to claim the >>> lock. >>> + * Because fl_blocker is explicitly set last during a delete, >>> it's >>> + * safe to locklessly test to see if it's NULL. If it is, >>> then we know >>> + * that no new locks can be inserted into its >>> fl_blocked_requests list, >>> + * and we can therefore avoid doing anything further as long >>> as that >>> + * list is empty. >>> + */ >>> + if (!smp_load_acquire(&waiter->fl_blocker) && >>> + list_empty(&waiter->fl_blocked_requests)) >>> + return status; >> >> Ack. This looks sane to me now. >> >> yangerkun - how did you find the original problem?\ > > While try to fix CVE-2019-19769, add some log in __locks_wake_up_blocks > help me to rebuild the problem soon. This help me to discern the problem > soon. > >> >> Would you mind using whatever stress test that caused commit >> 6d390e4b5d48 ("locks: fix a potential use-after-free problem when >> wakeup a waiter") with this patch? And if you did it analytically, >> you're a champ and should look at this patch too! > > I will try to understand this patch, and if it's looks good to me, will > do the performance test!
This patch looks good to me, with this patch, the bug '6d390e4b5d48 ("locks: fix a potential use-after-free problem when wakeup a waiter")' describes won't happen again. Actually, I find that syzkaller has report this bug before[1], and the log of it can help us to reproduce it with some latency in __locks_wake_up_blocks!
Also, some ltp testcases describes in [2] pass too with the patch!
For performance test, I have try to understand will-it-scale/lkp, but it seem a little complex to me, and may need some more time. So, Rong Chen, can you help to do this? Or the results may come a little later...
Thanks, ---- [1] https://syzkaller.appspot.com/bug?extid=922689db06e57b69c240 [2] https://lkml.org/lkml/2020/3/11/578
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