[Bug libc/4737] fork is not async-signal-safe

["morten+sources dot redhat dot com at afdelingp dot dk" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From morten+sources dot redhat dot com at afdelingp dot dk  2008-10-30 14:53 -------
Here is a bit more information.

It appears that this is more than one bug (or at least more than one lock). The
bug I hit is caused by __GI__IO_list_lock(). The bug which Nicholas Miell hit is
caused by ptmalloc_lock_all(), which is called via thread_atfork().

The following stack traces are from Ubuntu's libc6-2.7-10ubuntu3 glibc package.

When the deadlock is provoked by a fork() in the main loop:
#0  0xb7f3d410 in __kernel_vsyscall ()
#1  0xb7ebc033 in __lll_lock_wait_private () from /lib/tls/i686/cmov/libc.so.6
#2  0xb7e40a2d in _L_lock_2616 () from /lib/tls/i686/cmov/libc.so.6
#3  0xb7e3fd7d in __GI__IO_list_lock () from /lib/tls/i686/cmov/libc.so.6
#4  0xb7e6dd45 in fork () from /lib/tls/i686/cmov/libc.so.6
#5  0x080484ae in sighandler ()
#6  <signal handler called>
#7  0xb7e3fd77 in __GI__IO_list_lock () from /lib/tls/i686/cmov/libc.so.6
#8  0xb7e6dd45 in fork () from /lib/tls/i686/cmov/libc.so.6
#9  0x08048591 in main ()

When the deadlock is provoked by malloc()/free() in the main loop:
#0  0xb7f93410 in __kernel_vsyscall ()
#1  0xb7f12033 in __lll_lock_wait_private () from /lib/tls/i686/cmov/libc.so.6
#2  0xb7e9db4f in _L_lock_48 () from /lib/tls/i686/cmov/libc.so.6
#3  0xb7e9728b in ptmalloc_lock_all () from /lib/tls/i686/cmov/libc.so.6
#4  0xb7ec3f7f in fork () from /lib/tls/i686/cmov/libc.so.6
#5  0x0804850e in sighandler ()
#6  <signal handler called>
#7  0xb7e9971a in _int_free () from /lib/tls/i686/cmov/libc.so.6
#8  0xb7e9d4f0 in free () from /lib/tls/i686/cmov/libc.so.6
#9  0x08048600 in main ()

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                 CC|                            |morten+sources dot redhat
                   |                            |dot com at afdelingp dot dk


http://sourceware.org/bugzilla/show_bug.cgi?id=4737

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