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Date: Fri, 2 Nov 2018 13:11:00 +0800
From: "dirk@...iot.com" <dirk@...iot.com>
To: musl <musl@...ts.openwall.com>
Subject: Deadlock when calling fflush/fclose in multiple threads
Hi,
We got deadlock on fflush/fclose with musl-1.1.19 (openwrt 18.06). Actually we using lua's popen in mutiple threads, following is gdb trace.
I am new to musl libc source code, fflush(NULL) will call __ofl_lock and then try to lock and flush every stream, fclose will lock the stream and then __ofl_lock. The question is the fflush/fclose api thread-safe? What i have got from man document is that linux fflush/fclose is thread-safe api.
(gdb) info thread
Id Target Id Frame
* 1 LWP 2772 "skynet" __cp_end () at src/thread/i386/syscall_cp.s:31
2 LWP 2776 "skynet" __cp_end () at src/thread/i386/syscall_cp.s:31
3 LWP 2777 "skynet" __cp_end () at src/thread/i386/syscall_cp.s:31
4 LWP 2778 "skynet" 0xb7f95ad9 in __kernel_vsyscall ()
5 LWP 2779 "skynet" __cp_end () at src/thread/i386/syscall_cp.s:31
6 LWP 2780 "skynet" 0xb7f95ad9 in __kernel_vsyscall ()
7 LWP 2781 "skynet" 0xb7f95ad9 in __kernel_vsyscall ()
8 LWP 2782 "skynet" __cp_end () at src/thread/i386/syscall_cp.s:31
(gdb) thread 6
[Switching to thread 6 (LWP 2780)]
#0 0xb7f95ad9 in __kernel_vsyscall ()
(gdb) bt
#0 0xb7f95ad9 in __kernel_vsyscall ()
#1 0xb7fb1314 in __vsyscall () at src/internal/i386/syscall.s:19
#2 0xb7fe29a9 in __syscall4 (a4=0, a3=2781, a2=128, a1=136262812, n=240) at ./arch/i386/syscall_arch.h:37
#3 __wait (addr=0x81f349c, waiters=0x81f34a0, val=2781, priv=128) at src/thread/__wait.c:13
#4 0xb7fd7a52 in __lockfile (f=0x81f3450) at src/stdio/__lockfile.c:10
#5 0xb7fd829d in fflush (f=0x81f3450) at src/stdio/fflush.c:13
#6 0x0807129e in io_popen (L=0x81e5f04) at liolib.c:282
#7 0x0805a064 in luaD_precall (L=0x81e5f04, func=0x81e638c, nresults=2) at ldo.c:434
#8 0x080661f0 in luaV_execute (L=0x81e5f04) at lvm.c:1146
#9 0x08059dc1 in unroll (L=0x81e5f04, ud=0x0) at ldo.c:556
#10 0x080596bb in luaD_rawrunprotected (L=0x81e5f04, f=0x805a250 <resume>, ud=0xb778a5f8) at ldo.c:142
#11 0x0805a46d in lua_resume (L=0x81e5f04, from=0x81d8bd4, nargs=<optimized out>) at ldo.c:664
#12 0x0806f252 in auxresume (L=L@...ry=0x81d8bd4, co=co@...ry=0x81e5f04, narg=3) at lcorolib.c:39
#13 0x0806f5a5 in luaB_coresume (L=0x81d8bd4) at lcorolib.c:60
#14 0xb7732ca9 in timing_resume (L=0x81d8bd4) at lualib-src/lua-profile.c:134
#15 0x0805a064 in luaD_precall (L=0x81d8bd4, func=0x81e4144, nresults=-1) at ldo.c:434
#16 0x08066686 in luaV_execute (L=0x81d8bd4) at lvm.c:1162
#17 0x0805a348 in luaD_call (L=0x81d8bd4, func=0x81e4084, nResults=-1) at ldo.c:499
#18 0x0805a3ac in luaD_callnoyield (L=0x81d8bd4, func=0x81e4084, nResults=-1) at ldo.c:509
#19 0x080560e8 in f_call (L=0x81d8bd4, ud=0xb778a8e8) at lapi.c:944
#20 0x080596bb in luaD_rawrunprotected (L=0x81d8bd4, f=0x80560d0 <f_call>, ud=0xb778a8e8) at ldo.c:142
#21 0x0805a656 in luaD_pcall (L=0x81d8bd4, func=0x80560d0 <f_call>, u=0xb778a8e8, old_top=132, ef=0) at ldo.c:729
#22 0x08057969 in lua_pcallk (L=0x81d8bd4, nargs=5, nresults=-1, errfunc=0, ctx=0, k=0x806f070 <finishpcall>) at lapi.c:970
#23 0x0806f116 in luaB_pcall (L=0x81d8bd4) at lbaselib.c:424
#24 0x0805a064 in luaD_precall (L=0x81d8bd4, func=0x81e406c, nresults=2) at ldo.c:434
#25 0x080661f0 in luaV_execute (L=0x81d8bd4) at lvm.c:1146
#26 0x0805a348 in luaD_call (L=0x81d8bd4, func=0x81e4024, nResults=0) at ldo.c:499
#27 0x0805a3ac in luaD_callnoyield (L=0x81d8bd4, func=0x81e4024, nResults=0) at ldo.c:509
#28 0x080560e8 in f_call (L=0x81d8bd4, ud=0xb778abb8) at lapi.c:944
#29 0x080596bb in luaD_rawrunprotected (L=0x81d8bd4, f=0x80560d0 <f_call>, ud=0xb778abb8) at ldo.c:142
#30 0x0805a656 in luaD_pcall (L=0x81d8bd4, func=0x80560d0 <f_call>, u=0xb778abb8, old_top=36, ef=12) at ldo.c:729
#31 0x08057969 in lua_pcallk (L=0x81d8bd4, nargs=5, nresults=0, errfunc=1, ctx=0, k=0x0) at lapi.c:970
#32 0xb772978e in _cb (context=0x81da400, ud=0x81d8bd4, type=1, session=2, source=3, msg=0x81b1080, sz=2) at lualib-src/lua-skynet.c:75
#33 0x0804ecb1 in dispatch_message (ctx=ctx@...ry=0x81da400, msg=msg@...ry=0xb778ac80) at skynet-src/skynet_server.c:274
#34 0x0804f97a in skynet_context_message_dispatch (sm=0x815b2a0, q=0x81da470, weight=-1) at skynet-src/skynet_server.c:334
#35 0x080501a9 in thread_worker (p=0xbffffb9c) at skynet-src/skynet_start.c:163
#36 0xb7fe3fc5 in start (p=0xb778ad54) at src/thread/pthread_create.c:150
#37 0xb7fe2b3a in __clone () at src/thread/i386/clone.s:36
#38 0x00000000 in ?? ()
(gdb) thread 7
[Switching to thread 7 (LWP 2781)]
#0 0xb7f95ad9 in __kernel_vsyscall ()
(gdb) bt
#0 0xb7f95ad9 in __kernel_vsyscall ()
#1 0xb7fb1314 in __vsyscall () at src/internal/i386/syscall.s:19
#2 0xb7fe278b in __syscall3 (a3=-2147483646, a2=128, a1=-1207963496, n=240) at ./arch/i386/syscall_arch.h:30
#3 __futexwait (priv=128, val=-2147483646, addr=0xb7fff098 <ofl_lock>) at ./src/internal/pthread_impl.h:150
#4 __lock (l=0xb7fff098 <ofl_lock>) at src/thread/__lock.c:42
#5 0xb7fd9f30 in __ofl_lock () at src/stdio/ofl.c:9
#6 0xb7fd8144 in fclose (f=0x81f3450) at src/stdio/fclose.c:17
#7 0xb7fda4e2 in pclose (f=0x81f3450) at src/stdio/pclose.c:9
#8 0x0807130e in io_pclose (L=0x81f3034) at liolib.c:273
#9 0x0807090a in aux_close (L=0x81f3034) at liolib.c:205
#10 0x0805a064 in luaD_precall (L=0x81f3034, func=0x81f312c, nresults=0) at ldo.c:434
#11 0x080661f0 in luaV_execute (L=0x81f3034) at lvm.c:1146
#12 0x080596bb in luaD_rawrunprotected (L=0x81f3034, f=0x805a250 <resume>, ud=0xb77748c8) at ldo.c:142
#13 0x0805a46d in lua_resume (L=0x81f3034, from=0x81e6654, nargs=<optimized out>) at ldo.c:664
#14 0x0806f252 in auxresume (L=L@...ry=0x81e6654, co=co@...ry=0x81f3034, narg=0) at lcorolib.c:39
#15 0x0806f5a5 in luaB_coresume (L=0x81e6654) at lcorolib.c:60
#16 0xb7732ca9 in timing_resume (L=0x81e6654) at lualib-src/lua-profile.c:134
#17 0x0805a064 in luaD_precall (L=0x81e6654, func=0x81f09e4, nresults=-1) at ldo.c:434
#18 0x08066686 in luaV_execute (L=0x81e6654) at lvm.c:1162
#19 0x0805a348 in luaD_call (L=0x81e6654, func=0x81f0924, nResults=0) at ldo.c:499
#20 0x0805a3ac in luaD_callnoyield (L=0x81e6654, func=0x81f0924, nResults=0) at ldo.c:509
#21 0x080560e8 in f_call (L=0x81e6654, ud=0xb7774bb8) at lapi.c:944
#22 0x080596bb in luaD_rawrunprotected (L=0x81e6654, f=0x80560d0 <f_call>, ud=0xb7774bb8) at ldo.c:142
#23 0x0805a656 in luaD_pcall (L=0x81e6654, func=0x80560d0 <f_call>, u=0xb7774bb8, old_top=36, ef=12) at ldo.c:729
#24 0x08057969 in lua_pcallk (L=0x81e6654, nargs=5, nresults=0, errfunc=1, ctx=0, k=0x0) at lapi.c:970
#25 0xb772978e in _cb (context=0x81e6e00, ud=0x81e6654, type=1, session=1, source=0, msg=0x0, sz=0) at lualib-src/lua-skynet.c:75
#26 0x0804ecb1 in dispatch_message (ctx=ctx@...ry=0x81e6e00, msg=msg@...ry=0xb7774c80) at skynet-src/skynet_server.c:274
#27 0x0804f97a in skynet_context_message_dispatch (sm=0x815b2c0, q=0x81e6ec0, weight=-1) at skynet-src/skynet_server.c:334
#28 0x080501a9 in thread_worker (p=0xbffffba8) at skynet-src/skynet_start.c:163
#29 0xb7fe3fc5 in start (p=0xb7774d54) at src/thread/pthread_create.c:150
#30 0xb7fe2b3a in __clone () at src/thread/i386/clone.s:36
#31 0x00000000 in ?? ()
(gdb)
dirk@...iot.com
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