From: "Yannis Aribaud" <bugs@d6bell.net>
To: linux-kernel@vger.kernel.org
Subject: Re: divide error: 0000 [#1] SMP in task_numa_migrate - handle_mm_fault vanilla 4.4.6
Date: Wed, 22 Jun 2016 15:42:44 +0000 [thread overview]
Message-ID: <59700e91b7c0884329e904fc175031bc@rcube.hebserv.net> (raw)
In-Reply-To: <b04bc59cce59e2c027aefad2f1807d92@rcube.hebserv.net>
21 juin 2016 14:13 "Yannis Aribaud" <bugs@d6bell.net> a écrit:
> Hi everyone,
>
> I recently it this bug in the kernel using a vanilla 4.6.2 release.
> It seems that somewhere in the load average calculation a division by 0 occurs (see the stack trace
> at the end).
>
> [snipped]
>
> I'm not an expert at all but I suspect that is the issue's origin. Shouldn't the function
> cfs_rq_load_avg use an atomic_long_read() to avoid this ?
After digging a bit more, this can't be the problem as this function obviously can't return negative value.
I found that it can maybe come from the update_cfs_rq_load_avg function in the following block:
if (atomic_long_read(&cfs_rq->removed_load_avg)) {
s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
sa->load_avg = max_t(long, sa->load_avg - r, 0);
sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
removed_load = 1;
}
The max_t(long, sa->load_avg - r, 0) can result in a negative value keeped by the max_t function as the long would wrap up then generate a division by zero in task_h_load function.
Best regards,
--
Yannis Aribaud
next prev parent reply other threads:[~2016-06-22 15:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-21 12:13 divide error: 0000 [#1] SMP in task_numa_migrate - handle_mm_fault vanilla 4.4.6 Yannis Aribaud
2016-06-22 15:42 ` Yannis Aribaud [this message]
-- strict thread matches above, loose matches on Subject: below --
2016-03-17 18:38 Stefan Priebe
2016-03-17 18:45 ` Greg KH
2016-03-19 22:26 ` Vlastimil Babka
2016-03-20 21:27 ` Stefan Priebe
2016-03-20 21:41 ` Greg KH
2016-03-21 10:52 ` Stefan Priebe - Profihost AG
2016-03-21 13:38 ` Greg KH
2016-05-17 6:01 ` Stefan Priebe - Profihost AG
2016-05-17 9:21 ` Campbell Steven
2016-06-22 1:19 ` Campbell Steven
2016-06-22 6:13 ` Peter Zijlstra
2016-07-06 23:20 ` Campbell Steven
2016-07-07 7:42 ` Peter Zijlstra
2016-07-09 5:21 ` Greg KH
2016-07-11 22:33 ` Greg KH
2016-07-12 13:12 ` Peter Zijlstra
2016-07-13 0:26 ` Greg KH
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=59700e91b7c0884329e904fc175031bc@rcube.hebserv.net \
--to=bugs@d6bell.net \
--cc=linux-kernel@vger.kernel.org \
/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).