[Bug 929219]

[Law-redhat]

Based on just reading the code, I wonder if a one thread is mucking up
hst_map_handle.mapped behind the back of nscd_get_mapping.

nscd_get_nl_timestamp doesn't bother to grab the hst_map_handle lock and
calls into nscd_get_mapping which could potentially change
hst_map_handle.mapped to NO_MAPPING.

If this occurs after another thread had passed the NO_MAPPING check in
nscd_get_map_ref, but hasn't yet hit the atomic_decrement_val in
nscd_get_mapping then it could cause the failure mode reported in this
report (and several others across various distros, upstream kde and
possibly elsewhere).

That would also explain why the patch in c#2 works as well as the lack
of reproducability.

Vladimir/Paulo: I don't have a way to reproduce the problem here, but I
could pass along a patch to y'all if you're interested in testing my
theory.

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https://bugs.launchpad.net/bugs/929219

Title:
  chromium-browser crashed with SIGSEGV in __nscd_get_mapping()

Status in Embedded GLIBC:
  Confirmed
Status in The GNU C Library:
  Confirmed
Status in “chromium-browser” package in Ubuntu:
  Invalid
Status in “eglibc” package in Ubuntu:
  Triaged
Status in “chromium-browser” source package in Precise:
  Invalid
Status in “eglibc” source package in Precise:
  Triaged

Bug description:
  updated latest - rebooted and tried to open chromium, no such luck

  ProblemType: Crash
  DistroRelease: Ubuntu 12.04
  Package: chromium-browser 16.0.912.77~r118311-0ubuntu1
  ProcVersionSignature: Ubuntu 3.2.0-14.23-generic 3.2.3
  Uname: Linux 3.2.0-14-generic i686
  ApportVersion: 1.91-0ubuntu1
  Architecture: i386
  CheckboxSubmission: 8617bffd198177508bf030f94c880aca
  CheckboxSystem: bb422ca46d02494cdbc459927a98bc2f
  CrashCounter: 1
  CrashDB: ubuntu
  Date: Thu Feb  9 00:48:53 2012
  Desktop-Session:
   DESKTOP_SESSION = ubuntu
   XDG_CONFIG_DIRS = /etc/xdg/xdg-ubuntu:/etc/xdg
   XDG_DATA_DIRS = /usr/share/ubuntu:/usr/share/gnome:/usr/local/share/:/usr/share/
  Env:
   MOZ_PLUGIN_PATH = None
   LD_LIBRARY_PATH = None
  ExecutablePath: /usr/lib/chromium-browser/chromium-browser
  InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
  ProcCmdline: /usr/lib/chromium-browser/chromium-browser
  ProcEnviron:
   
  SegvAnalysis:
   Segfault happened at: 0xb7db005:	lock xadd %ecx,0xc(%eax)
   PC (0x0b7db005) ok
   source "%ecx" ok
   destination "0xc(%eax)" (0x0000000b) not located in a known VMA region (needed writable region)!
   Stack memory exhausted (SP below stack segment)
  SegvReason: writing NULL VMA
  Signal: 11
  SourcePackage: chromium-browser
  StacktraceTop:
   ?? () from /lib/i386-linux-gnu/libc.so.6
   ?? () from /lib/i386-linux-gnu/libc.so.6
   ?? () from /lib/i386-linux-gnu/libc.so.6
   ?? () from /lib/i386-linux-gnu/libc.so.6
   gethostbyname2_r () from /lib/i386-linux-gnu/libc.so.6
  ThirdParty: True
  Title: chromium-browser crashed with SIGSEGV in gethostbyname2_r()
  UpgradeStatus: Upgraded to precise on 2012-02-05 (3 days ago)
  UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
  chromium-default: CHROMIUM_FLAGS=""

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