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  • Committer: Package Import Robot
  • Author(s): Matthias Klose
  • Date: 2011-10-04 17:48:26 UTC
  • mfrom: (216.1.23 oneiric)
  • Revision ID: package-import@ubuntu.com-20111004174826-2cyb9ewn3ucymlsx
Tags: 2.13-20ubuntu5
https://launchpad.net/bugs/853688
libc6-dev: Don't break the current {gnat,gcj}-4.4-base versons. LP: #853688.

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debian/patches/any/local-nscd-NO_MAPPING.diff
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Description: Fix thread locking for __nscd_get_mapping
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 This patch should solve occasional chromium-browser crashes,
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 and other possibly-related (ktorrent?) crashes from thread
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 corruption in __nscd_get_mapping.
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Author: Jeff Law <law@redhat.com>
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Bug: http://sourceware.org/bugzilla/show_bug.cgi?id=13594
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Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+bug/929219
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diff -rup c/nscd/nscd_gethst_r.c d/nscd/nscd_gethst_r.c
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--- c/nscd/nscd_gethst_r.c      2012-01-01 05:16:32.000000000 -0700
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+++ d/nscd/nscd_gethst_r.c      2012-03-28 10:45:51.546600822 -0600
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@@ -101,9 +101,27 @@ libc_freeres_fn (hst_map_free)
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 uint32_t
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 __nscd_get_nl_timestamp (void)
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 {
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+  uint32_t retval;
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   if (__nss_not_use_nscd_hosts != 0)
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     return 0;
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+  int cnt = 0;
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+  /* __nscd_get_mapping can change hst_map_handle.mapped to NO_MAPPING.
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+   However, __nscd_get_mapping assumes the prior value was not NO_MAPPING.
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+   Thus we have to acquire the lock to prevent this thread from changing
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+   hst_map_handle.mapped to NO_MAPPING while another thread is inside
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+    __nscd_get_mapping.  */
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+  while (__builtin_expect
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+        (atomic_compare_and_exchange_val_acq (&__hst_map_handle.lock,
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+                                              1, 0) != 0, 0))
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+    {
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+      // XXX Best number of rounds?
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+      if (__builtin_expect (++cnt > 5, 0))
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+       return 0;
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+
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+      atomic_delay ();
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+    }
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+
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   struct mapped_database *map = __hst_map_handle.mapped;
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   if (map == NULL
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@@ -113,9 +131,14 @@ __nscd_get_nl_timestamp (void)
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     map = __nscd_get_mapping (GETFDHST, "hosts", &__hst_map_handle.mapped);
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   if (map == NO_MAPPING)
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-    return 0;
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+    retval =  0;
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+  else
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+    retval =  map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
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+
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+  /* Release the lock.  */
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+  __hst_map_handle.lock = 0;
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-  return map->head->extra_data[NSCD_HST_IDX_CONF_TIMESTAMP];
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+  return retval;
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 }
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