Package: pagein
Version: 0.00.03-1
Severity: important
Dear Maintainer,
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From: Ben Wiederhake <[email protected]>
To: Debian Bug Tracking System <[email protected]>
Subject: pagein: Segfaults roughly every 1 in ten executions
Message-ID: <149796559606.22041.12836038062408551702.reportbug@bewied-eeepc>
X-Mailer: reportbug 7.1.7
Date: Tue, 20 Jun 2017 15:33:16 +0200
Package: pagein
Version: 0.00.03-1
Severity: normal
Dear Maintainer,
How to reproduce:
user@machine:/$ sudo -s
root@machine:/# pagein -a -v
root@machine:/# pagein -a -v
root@machine:/# pagein -a -v
root@machine:/# pagein -a -v
# You get the idea.
Expected results:
Runs without issues, as described in the man page
Actual results:
Sometimes, it crashed without apparent reason.
Potentially relevant:
- 'pagein -a' also crashes, and more reliably.
- Architecture is i686.
- 1 GiB of physical RAM, and "swap in use" is greater than "mem free" according
to /usr/bin/free
(I know, that just shuffles around the pages; but still, it shouldn't
segfault.)
- Running this on a specific process, e.g. smartd (which runs as root,
and happened to be PID 510 during my tests) also exhibits the bug.
- Running this on a specific "luser" process as non-root also exhibits the bug.
- Adding a bit of printf debugging reveals which process it's looking at when
it crashes:
Sample from three attempts: smartd (510), policykit (574), reportbug (22041),
exim4 (907)
I don't see any pattern.
- Recompiling from source (apt-get source and 'make' instead of using Debian
tools)
also segfaults. I have the impression that it's more seldom, but that may be
subjective.
- Running this in gdb apparently "fixes it".
(Set a breakpoint on exit with 'run -p 510 -v', fetch a cup of hot chocolate,
see that it doesn't crash even after a hundred runs.)
- Running this in valgrind apparently "fixes it".
- Apparently valgrind and gdb change the timing a bit, and the segfault is due
to a race
condition of some kind. That could even explain the slight increase in
reliability after adding
printf's into the loop of 'pagein_all_procs'.
- If that's the case, then '--show-mismatched-frees=no --keep-stacktraces=none
--leak-resolution=low'
doesn't make valgrind fast enough to cause the segfault there.
- Doing some printf-debugging, it seems that it always crashes "towards the
end", but still in 'pagein_proc'.
Any further printf-debugging slows the program down sufficiently to prevent
it from crashing.
What else could I test?
Cheers,
Ben Wiederhake
-- System Information:
Debian Release: 9.0
APT prefers testing
APT policy: (500, 'testing'), (500, 'stable')
Architecture: i386 (i686)
Kernel: Linux 4.9.0-3-686-pae (SMP w/2 CPU cores)
Locale: LANG=de_DE.utf8, LC_CTYPE=de_DE.utf8 (charmap=UTF-8),
LANGUAGE=de_DE.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages pagein depends on:
ii libc6 2.24-11
pagein recommends no packages.
pagein suggests no packages.
-- no debconf information
-- System Information:
Debian Release: 9.0
APT prefers testing
APT policy: (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 4.9.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8),
LANGUAGE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages pagein depends on:
ii libc6 2.24-11
pagein recommends no packages.
pagein suggests no packages.
