[Libunwind-devel] deadlock in get_rs_cache

[Howard Chu]

Using libunwind 1.1 on SLES with my own malloc tracer, I get a deadlock in 
various places, e.g.:

#0  0x00007f65311a2324 in __lll_lock_wait () from /lib64/libpthread.so.0

#1  0x00007f653119d669 in _L_lock_1008 () from /lib64/libpthread.so.0

#2  0x00007f653119d47e in pthread_mutex_lock () from /lib64/libpthread.so.0

#3  0x00007f6530c05622 in get_rs_cache (saved_maskp=<optimized out>,

    as=<optimized out>) at dwarf/Gparser.c:531

#4  _ULx86_64_dwarf_find_save_locs (c=0x7ffd68e96b10) at dwarf/Gparser.c:853

#5  0x00007f6530c05839 in _ULx86_64_dwarf_step (

    c=0x7f6530e0d220 <local_addr_space+96>) at dwarf/Gstep.c:34

#6  0x00007f6530c01dd4 in _ULx86_64_step (

    cursor=0x7f6530e0d220 <local_addr_space+96>) at x86_64/Gstep.c:71

#7  0x00007f65323ece20 in ml_backtrace (stk=0x8300fc0, stknum=24) at mleak.c:63

#8  0x00007f65323ed332 in malloc (size=25) at mleak.c:231

#9  0x00007f6537613f02 in local_strdup () from /lib64/ld-linux-x86-64.so.2

#10 0x00007f6537616c86 in _dl_map_object () from /lib64/ld-linux-x86-64.so.2

#11 0x00007f6537621400 in dl_open_worker () from /lib64/ld-linux-x86-64.so.2

#12 0x00007f653761ce86 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2

#13 0x00007f6537620e3b in _dl_open () from /lib64/ld-linux-x86-64.so.2

#14 0x00007f6531bbff9b in dlopen_doit () from /lib64/libdl.so.2

#15 0x00007f653761ce86 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2

#16 0x00007f6531bc033c in _dlerror_run () from /lib64/libdl.so.2

#17 0x00007f6531bbff01 in dlopen@@GLIBC_2.2.5 () from /lib64/libdl.so.2

The tracer is at https://github.com/hyc/mleak

I haven't been able to identify where get_rs_cache was called previously, but 
it strikes me that just using a recursive mutex would make this problem go 
away. See attached patch.

--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/

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