From: Nico Pache <npache@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Rafael Aquini <aquini@redhat.com>,
Waiman Long <longman@redhat.com>, Baoquan He <bhe@redhat.com>,
Christoph von Recklinghausen <crecklin@redhat.com>,
Don Dutile <ddutile@redhat.com>,
"Herton R . Krzesinski" <herton@redhat.com>,
David Rientjes <rientjes@google.com>,
Michal Hocko <mhocko@suse.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@redhat.com>, Joel Savitz <jsavitz@redhat.com>,
Darren Hart <dvhart@infradead.org>,
stable@kernel.org
Subject: Re: [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head
Date: Mon, 11 Apr 2022 19:51:50 -0400 [thread overview]
Message-ID: <1a7944c7-d717-d5af-f71d-92326f7bb7f6@redhat.com> (raw)
In-Reply-To: <87k0bzk7e5.ffs@tglx>
On 4/8/22 09:54, Thomas Gleixner wrote:
> On Fri, Apr 08 2022 at 04:41, Nico Pache wrote:
>> On 4/8/22 04:15, Peter Zijlstra wrote:
>>>>
>>>> The following case can still fail:
>>>> robust head (skipped) -> private lock (reaped) -> shared lock (skipped)
>>>
>>> This is still all sorts of confused.. it's a list head, the entries can
>>> be in any random other VMA. You must not remove *any* user memory before
>>> doing the robust thing. Not removing the VMA that contains the head is
>>> pointless in the extreme.
>> Not sure how its pointless if it fixes all the different reproducers we've
>> written for it. As for the private lock case we stated here, we havent been able
>> to reproduce it, but I could see how it can be a potential issue (which is why
>> its noted).
>
> The below reproduces the problem nicely, i.e. the lock() in the parent
> times out. So why would the OOM killer fail to cause the same problem
> when it reaps the private anon mapping where the private futex sits?
>
> If you revert the lock order in the child the robust muck works.
Thanks for the reproducer Thomas :)
I think I need to re-up my knowledge around COW and how it effects that stack.
There are increased oddities when you add the pthread library that I cant fully
wrap my head around at the moment.
My confusion lies in how the parent/child share a robust list here, but they
obviously do. In my mind the mut_s would be different in the child/parent after
the fork and pthread_mutex_init (and friends) are done in the child.
Thanks!
-- Nico
>
> Thanks,
>
> tglx
> ---
> #include <errno.h>
> #include <fcntl.h>
> #include <pthread.h>
> #include <time.h>
> #include <stdio.h>
> #include <string.h>
> #include <unistd.h>
>
> #include <sys/types.h>
> #include <sys/mman.h>
>
> static char n[4096];
>
> int main(void)
> {
> pthread_mutexattr_t mat_s, mat_p;
> pthread_mutex_t *mut_s, *mut_p;
> pthread_barrierattr_t ba;
> pthread_barrier_t *b;
> struct timespec to;
> void *pri, *shr;
> int r;
>
> shr = mmap(NULL, sizeof(n), PROT_READ | PROT_WRITE,
> MAP_SHARED | MAP_ANONYMOUS, -1, 0);
>
> pthread_mutexattr_init(&mat_s);
> pthread_mutexattr_setrobust(&mat_s, PTHREAD_MUTEX_ROBUST);
> mut_s = shr;
> pthread_mutex_init(mut_s, &mat_s);
>
> pthread_barrierattr_init(&ba);
> pthread_barrierattr_setpshared(&ba, PTHREAD_PROCESS_SHARED);
> b = shr + 1024;
> pthread_barrier_init(b, &ba, 2);
>
> if (!fork()) {
> pri = mmap(NULL, 1<<20, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> pthread_mutexattr_init(&mat_p);
> pthread_mutexattr_setpshared(&mat_p, PTHREAD_PROCESS_PRIVATE);
> pthread_mutexattr_setrobust(&mat_p, PTHREAD_MUTEX_ROBUST);
> mut_p = pri;
> pthread_mutex_init(mut_p, &mat_p);
>
> // With lock order s, p parent gets timeout
> // With lock order p, s parent gets owner died
> pthread_mutex_lock(mut_s);
> pthread_mutex_lock(mut_p);
> // Remove unmap and lock order does not matter
> munmap(pri, sizeof(n));
> pthread_barrier_wait(b);
> printf("child gone\n");
> } else {
> pthread_barrier_wait(b);
> printf("parent lock\n");
> clock_gettime(CLOCK_REALTIME, &to);
> to.tv_sec += 1;
> r = pthread_mutex_timedlock(mut_s, &to);
> printf("parent lock returned: %s\n", strerror(r));
> }
> return 0;
> }
>
next prev parent reply other threads:[~2022-04-11 23:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-08 3:28 [PATCH v8] oom_kill.c: futex: Don't OOM reap the VMA containing the robust_list_head Nico Pache
2022-04-08 8:15 ` Peter Zijlstra
2022-04-08 8:37 ` Thomas Gleixner
2022-04-08 8:52 ` Nico Pache
2022-04-08 9:36 ` Michal Hocko
2022-04-08 9:40 ` Nico Pache
2022-04-08 9:59 ` Michal Hocko
2022-04-08 10:36 ` Nico Pache
2022-04-08 10:51 ` Michal Hocko
2022-04-08 11:26 ` Nico Pache
2022-04-08 11:48 ` Michal Hocko
2022-04-08 8:41 ` Nico Pache
2022-04-08 13:54 ` Thomas Gleixner
2022-04-08 16:13 ` Joel Savitz
2022-04-08 21:41 ` Thomas Gleixner
2022-04-11 6:48 ` Michal Hocko
2022-04-11 7:47 ` Thomas Gleixner
2022-04-11 9:08 ` Michal Hocko
2022-04-12 0:02 ` Nico Pache
2022-04-13 16:00 ` Nico Pache
2022-04-11 23:51 ` Nico Pache [this message]
2022-04-12 16:20 ` Thomas Gleixner
2022-04-12 17:03 ` Nico Pache
2022-04-08 14:41 ` kernel test robot
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=1a7944c7-d717-d5af-f71d-92326f7bb7f6@redhat.com \
--to=npache@redhat.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=aquini@redhat.com \
--cc=bhe@redhat.com \
--cc=crecklin@redhat.com \
--cc=dave@stgolabs.net \
--cc=ddutile@redhat.com \
--cc=dvhart@infradead.org \
--cc=herton@redhat.com \
--cc=jsavitz@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=longman@redhat.com \
--cc=mhocko@suse.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rientjes@google.com \
--cc=stable@kernel.org \
--cc=tglx@linutronix.de \
/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: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).