linux-kernel - Re: frequent lockups in 3.18rc4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 3 Dec 2014 21:49:04 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Chris Mason <clm@...com>, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Dec 3, 2014 at 7:15 PM, Chris Mason <clm@...com> wrote:
>
> One guess is that trinity is generating a huge number of tlb
> invalidations over sparse and horrible ranges.  Perhaps the old code was
> falling back to full tlb flushes before Dave Hansen's string of fixes?

Hmm. I agree that we've had some of the backtraces look like TLB
flushing might be involved. Not all, though. And I'm not seeing where
a loop over up to 33 pages should matter over doing a full TLB flush.

What *might* matter is if we somehow get that number wrong, and the loops like

                        addr = f->flush_start;
                        while (addr < f->flush_end) {
                                __flush_tlb_single(addr);
                                addr += PAGE_SIZE;
                        }

ends up looping a *lot* due to some bug, and then the IPI itself would
take so long that the watchdog could trigger.

But I do not see how that could actually happen. As far as I can tell,
either the number of pages is limited to less than 33, or we have that
 TLB_FLUSH_ALL case.

Do  you see something I don't?

                  Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/