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Date: Fri, 7 Dec 2018 16:51:03 -0600
From: "A. Wilcox" <awilfox@...lielinux.org>
To: musl@...ts.openwall.com
Subject: Re: aio_cancel segmentation fault for in progress write
 requests

On 12/07/18 14:35, Markus Wichmann wrote:
> On Fri, Dec 07, 2018 at 01:13:44PM -0600, A. Wilcox wrote:
>> So, my best theory is that running inside a debugger (gdb, valgrind)
>> makes it slow enough that it no longer races.
> 
> Two ideas to investigate further. 1: Produce a coredump ("ulimit -c
> unlimited"). That won't interfere with timing, but I have no clue if
> coredumps work with multithreading.

Core was generated by `./aioWrite '.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  __cp_end () at src/thread/powerpc64/syscall_cp.s:32
32      src/thread/powerpc64/syscall_cp.s: No such file or directory.
[Current thread is 1 (LWP 5507)]
(gdb) bt
#0  __cp_end () at src/thread/powerpc64/syscall_cp.s:32
#1  0x00003fffa768f2a4 in __syscall_cp_c (nr=180, u=512512, v=0, w=0,
x=0, y=0, z=0) at src/thread/pthread_cancel.c:35
#2  0x00003fffa768e008 in __syscall_cp (nr=<optimized out>, u=<optimized
out>, v=<optimized out>, w=<optimized out>, x=<optimized out>,
y=<optimized out>, z=<optimized out>) at src/thread/__syscall_cp.c:20
#3  0x00003fffa76969f4 in pwrite (fd=<optimized out>, buf=<optimized
out>, size=<optimized out>, ofs=<optimized out>) at src/unistd/pwrite.c:7
#4  0x00003fffa763eddc in io_thread_func (ctx=<optimized out>) at
src/aio/aio.c:240
#5  0x00003fffa768f76c in start (p=0x3fffa76e8af8) at
src/thread/pthread_create.c:147
#6  0x00003fffa769b608 in __clone () at src/thread/powerpc64/clone.s:43
(gdb) thread 2
[Switching to thread 2 (LWP 5506)]
#0  0x00003fffa7637144 in __syscall4 (d=0, c=-1, b=128, a=512, n=221) at
./arch/powerpc64/syscall_arch.h:54
54      ./arch/powerpc64/syscall_arch.h: No such file or directory.
(gdb) bt
#0  0x00003fffa7637144 in __syscall4 (d=0, c=-1, b=128, a=512, n=221) at
./arch/powerpc64/syscall_arch.h:54
#1  __wait (addr=0x200, waiters=0x0, val=<optimized out>,
priv=<optimized out>) at src/thread/__wait.c:13
#2  0x00003fffa763f07c in aio_cancel (fd=<optimized out>,
cb=0x3fffffafd2b8) at src/aio/aio.c:356
#3  0x000000012034c044 in main ()


221 is SYS_futex.  Wow, that looks wrong.

Best,
--arw

-- 
A. Wilcox (awilfox)
Project Lead, Adélie Linux
https://www.adelielinux.org



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