linux-kernel - Re: [PATCH 1/1] perf tools: Fix thread_map event synthesizing in top and record

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]

Message-ID: <x49aai38yqa.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 10 Feb 2011 14:40:29 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Tom Zanussi <tzanussi@...il.com>
Subject: Re: [PATCH 1/1] perf tools: Fix thread_map event synthesizing in top and record

Arnaldo Carvalho de Melo <acme@...radead.org> writes:

> From: Arnaldo Carvalho de Melo <acme@...hat.com>
>
> Jeff Moyer reported these messages:
>
>   Warning:  ... trying to fall back to cpu-clock-ticks
>
> couldn't open /proc/-1/status
> couldn't open /proc/-1/maps
> [ls output]
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.008 MB perf.data (~363 samples) ]
>
> That lead me and David Ahern to see that something was fishy on the thread
> synthesizing routines, at least for the case where the workload is started
> from 'perf record', as -1 is the default for target_tid in 'perf record --tid'
> parameter, so somehow we were trying to synthesize the PERF_RECORD_MMAP and
> PERF_RECORD_COMM events for the thread -1, a bug.
>
> So I investigated this and noticed that when we introduced support for
> recording a process and its threads using --pid some bugs were introduced and
> that the way to fix it was to instead of passing the target_tid to the event
> synthesizing routines we should better pass the thread_map that has the list of
> threads for a --pid or just the single thread for a --tid.

Thanks for looking into this, acme.  Honestly, I can't for the life of
me figure out from your description how this problem would have affected
systems.  The fix makes the warnings go away, but I am still left with
the hung system I originally reported.

So, what does this patch actually fix?  And do you or others have any
interest in trying to work out why perf is hanging my system?

Thanks!
Jeff
--
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/