Reported by Lakshmipathi. 
The crash happened on a replicated volume. the client crashed due to possible split-brain errors.

Valgrind log says
==8508== Invalid read of size 8
==8508==    at 0x81D65FA: ioc_open_cbk (io-cache.c:554)
==8508==    by 0x7FC680F: ra_open_cbk (read-ahead.c:119)
==8508==    by 0x7DB9936: wb_open_cbk (write-behind.c:1390)
==8508==    by 0x7B5CB6B: afr_open_cbk (afr-open.c:210)
==8508==    by 0x790FB27: client3_1_open_cbk (client3_1-fops.c:375)
==8508==    by 0x4EA0904: rpc_clnt_handle_reply (rpc-clnt.c:789)
==8508==    by 0x4EA0C51: rpc_clnt_notify (rpc-clnt.c:902)
==8508==    by 0x4E9CD87: rpc_transport_notify (rpc-transport.c:498)
==8508==    by 0x8E46212: socket_event_poll_in (socket.c:1675)
==8508==    by 0x8E46796: socket_event_handler (socket.c:1790)
==8508==    by 0x4C561E3: event_dispatch_epoll_handler (event.c:794)
==8508==    by 0x4C56406: event_dispatch_epoll (event.c:856)
==8508==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

[2011-09-26 11:56:51.620256] I [afr-self-heal-common.c:713:afr_mark_sources] 0-afr-replicate-0: split-brain possible, no source detected
[2011-09-26 11:56:51.620546] E [afr-self-heal-data.c:697:afr_sh_data_fix] 0-afr-replicate-0: Unable to self-heal contents of '/run8525/ltp/large_file' (possible split-brain). Please delete the file from all but the preferred subvolume.
[2011-09-26 11:56:51.629579] E [afr-self-heal-common.c:2009:afr_self_heal_completion_cbk] 0-afr-replicate-0: background  data missing-entry gfid self-heal failed on /run8525/ltp/large_file
[2011-09-26 12:04:36.273144] W [client3_1-fops.c:554:client3_1_rmdir_cbk] 0-afr-client-0: remote operation failed: Directory not empty
[2011-09-26 12:04:36.293733] W [client3_1-fops.c:554:client3_1_rmdir_cbk] 0-afr-client-1: remote operation failed: Directory not empty
[2011-09-26 12:05:16.861358] W [client3_1-fops.c:554:client3_1_rmdir_cbk] 0-afr-client-0: remote operation failed: Directory not empty
[2011-09-26 12:05:16.869475] W [client3_1-fops.c:554:client3_1_rmdir_cbk] 0-afr-client-1: remote operation failed: Directory not empty
[2011-09-26 12:05:21.898045] I [afr-self-heal-common.c:713:afr_mark_sources] 0-afr-replicate-0: split-brain possible, no source detected
[2011-09-26 12:05:21.900249] W [stat-prefetch.c:2634:sp_unlink_helper] 0-afr-stat-prefetch: lookup-behind has failed for path (/run8525/ltp/large_file)(Input/output error), unwinding unlink call waiting on it
[2011-09-26 12:05:21.901963] W [fuse-bridge.c:908:fuse_unlink_cbk] 0-glusterfs-fuse: 91779: UNLINK() /run8525/ltp/large_file => -1 (Input/output error)
pending frames:
frame : type(1) op(OPEN)
frame : type(1) op(OPEN)
frame : type(1) op(OPEN)
frame : type(1) op(OPEN)
frame : type(1) op(OPEN)
frame : type(1) op(OPEN)

patchset: git://git.gluster.com/glusterfs.git
signal received: 11
time of crash: 2011-09-26 12:05:21
configuration details:
argp 1
backtrace 1
dlfcn 1
fdatasync 1
libpthread 1
llistxattr 1
setfsid 1
spinlock 1
epoll.h 1
xattr.h 1
st_atim.tv_nsec 1
package-string: glusterfs 3git
/lib64/libc.so.6[0x3d920332f0]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/xlator/performance/io-cache.so(ioc_open_cbk+0x125)[0x81d65fa]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/xlator/performance/read-ahead.so(ra_open_cbk+0x458)[0x7fc6810]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/xlator/performance/write-behind.so(wb_open_cbk+0x356)[0x7db9937]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/xlator/cluster/replicate.so(afr_open_cbk+0x676)[0x7b5cb6c]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/xlator/protocol/client.so(client3_1_open_cbk+0x433)[0x790fb28]
/opt/glusterfs/nightly_valgrind/lib/libgfrpc.so.0(rpc_clnt_handle_reply+0x211)[0x4ea0905]
/opt/glusterfs/nightly_valgrind/lib/libgfrpc.so.0(rpc_clnt_notify+0x285)[0x4ea0c52]
/opt/glusterfs/nightly_valgrind/lib/libgfrpc.so.0(rpc_transport_notify+0x130)[0x4e9cd88]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/rpc-transport/socket.so(socket_event_poll_in+0x54)[0x8e46213]
/opt/glusterfs/nightly_valgrind/lib/glusterfs/3git/rpc-transport/socket.so(socket_event_handler+0x21d)[0x8e46797]
/opt/glusterfs/nightly_valgrind/lib/libglusterfs.so.0[0x4c561e4]
/opt/glusterfs/nightly_valgrind/lib/libglusterfs.so.0[0x4c56407]
/opt/glusterfs/nightly_valgrind/lib/libglusterfs.so.0(event_dispatch+0x88)[0x4c56792]
/opt/glusterfs/nightly_valgrind/sbin/glusterfs(main+0x238)[0x407a00]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x3d9201ea4d]
/opt/glusterfs/nightly_valgrind/sbin/glusterfs[0x403ce9]


Lakshmipathi will be updating the proper commit-id later.

Trying to reproduce this on master. Will update soon.

unable to reproduce this on master "b6eee04da4a699c7cd850bf2121825cc67f14707" with replicate on master.