HANG during mem query for leak scan in gap and vortex

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:58:21_

PR 558030

during perf runs on Linux of Dr. Memory w/ default options, I had gap and
vortex hit this at exit and spin:

(gdb) bt
#0 0xf76c801f in syscall_0args () from /work/dr/stat/exports/lib32/release/libdynamorio.so
#1 0x21bd1ac8 in ?? ()
#2 0x098bb318 in ?? ()
#3 0x21bd1a98 in ?? ()
#4 0xf76fc69c in backtrace_symbols_fd () from /work/dr/stat/exports/lib32/release/libdynamorio.so
#5 0xf76d13f4 in read_syscall (nbytes= , buf= , fd= )
at /work/dr/stat/opensource/core/linux/os.c:2473
#6 os_read (nbytes= , buf= , fd= )
at /work/dr/stat/opensource/core/linux/os.c:2535
#7 maps_iterator_next (nbytes= , buf= , fd= )
at /work/dr/stat/opensource/core/linux/os.c:5292
#8 0xf76d4051 in query_memory_ex_from_os (pc=0x98bb318 "UUUU\002", info=0x21bd1b70)
at /work/dr/stat/opensource/core/linux/os.c:6345
#9 0xf76cce54 in dr_query_memory_ex (pc=0x98bb318 "UUUU\002", info=0x21bd1b70)
at /work/dr/stat/opensource/core/x86/instrument.c:2216
#10 0xf7579b3d in check_reachability_helper ()
from /work/dr/stat/exports_drmemory/drmemory/bin/bin32/release/libdrmemory.so
#11 0xf7579dea in leak_scan_for_leaks () from /work/dr/stat/exports_drmemory/drmemory/bin/bin32/release/libdrmemory.so
#12 0xf757151b in check_reachability () from /work/dr/stat/exports_drmemory/drmemory/bin/bin32/release/libdrmemory.so
#13 0xf754c846 in event_exit () from /work/dr/stat/exports_drmemory/drmemory/bin/bin32/release/libdrmemory.so
#14 0xf76ce41e in instrument_exit () at /work/dr/stat/opensource/core/x86/instrument.c:602
#15 0xf7636895 in dynamo_process_exit () at /work/dr/stat/opensource/core/dynamo.c:1352
#16 0xf76c7f78 in cat_done_saving_dstack () from /work/dr/stat/exports/lib32/release/libdynamorio.so
#17 0xf76c7fd7 in cat_have_lock () from /work/dr/stat/exports/lib32/release/libdynamorio.s

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=185_