Date: Tue, 6 Dec 2016 16:30:14 +0100 From: Dimitri Staessens <dimitri.staessens@intec.ugent.be> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-threads@freebsd.org Subject: Re: Unlocking a robust mutex in a cleanup handler Message-ID: <35726dbb-75f7-682d-ad41-c78b96675485@intec.ugent.be> In-Reply-To: <20161206144812.GS54029@kib.kiev.ua> References: <119e59d4-6125-f313-e6e6-67055a15d224@intec.ugent.be> <20161206112558.GN54029@kib.kiev.ua> <6a7139cd-b6db-d078-ee5e-b7c590eb13d1@intec.ugent.be> <20161206144812.GS54029@kib.kiev.ua>
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Dear Konstantin,
I didn't get the error, but on my machine the thread never exists the
condwait when the pthread_cancel is called.
gdb output:
$ sudo gdb ./robust_test 3246
GNU gdb 6.1.1 [FreeBSD]
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welcome to change it and/or distribute copies of it under certain
conditions.
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This GDB was configured as "amd64-marcel-freebsd"...(no debugging
symbols found)...
Attaching to program: /usr/home/dstaesse/robust_test, process 3246
Reading symbols from /lib/libthr.so.3...Reading symbols from
/usr/lib/debug//lib/libthr.so.3.debug...done.
[New Thread 801416500 (LWP 100404/robust_test)]
[New Thread 801416000 (LWP 100313/robust_test)]
done.
Loaded symbols for /lib/libthr.so.3
Reading symbols from /usr/lib/librt.so.1...done.
Loaded symbols for /usr/lib/librt.so.1
Reading symbols from /lib/libc.so.7...done.
Loaded symbols for /lib/libc.so.7
Reading symbols from /libexec/ld-elf.so.1...done.
Loaded symbols for /libexec/ld-elf.so.1
[Switching to Thread 801416000 (LWP 100313/robust_test)]
0x00000008008386ac in _umtx_op_err () from /lib/libthr.so.3
(gdb) info threads
* 2 Thread 801416000 (LWP 100313/robust_test) 0x00000008008386ac in
_umtx_op_err () from /lib/libthr.so.3
1 Thread 801416500 (LWP 100404/robust_test) _thr_ast
(curthread=0x801416500) at /usr/src/lib/libthr/thread/thr_sig.c:271
Current language: auto; currently minimal
(gdb) bt
#0 0x00000008008386ac in _umtx_op_err () from /lib/libthr.so.3
#1 0x0000000800834df6 in join_common (pthread=<value optimized out>,
thread_return=<value optimized out>, abstime=<value optimized out>)
at /usr/src/lib/libthr/thread/thr_join.c:125
#2 0x0000000000401186 in main ()
(gdb) thread 1
[Switching to thread 1 (Thread 801416500 (LWP 100404/robust_test))]#0
_thr_ast (curthread=0x801416500)
at /usr/src/lib/libthr/thread/thr_sig.c:271
271 check_suspend(curthread);
(gdb) bt
#0 _thr_ast (curthread=0x801416500) at
/usr/src/lib/libthr/thread/thr_sig.c:271
#1 0x0000000800837a5b in __thr_pshared_offpage (key=<value optimized
out>, doalloc=<value optimized out>)
at /usr/src/lib/libthr/thread/thr_pshared.c:86
#2 0x00000008008363cb in cond_wait_common (cond=<value optimized out>,
mutex=0x800643004, abstime=0x0, cancel=1)
at /usr/src/lib/libthr/thread/thr_cond.c:349
#3 0x0000000000400ff2 in blockfunc ()
#4 0x000000080082ab55 in thread_start (curthread=<value optimized out>)
at /usr/src/lib/libthr/thread/thr_create.c:289
#5 0x0000000000000000 in ?? ()
(gdb)
cheers,
Dimitri
On 12/06/16 15:48, Konstantin Belousov wrote:
> On Tue, Dec 06, 2016 at 03:17:41PM +0100, Dimitri Staessens wrote:
>> Dear Konstantin,
>>
>> thanks for your immediate response. Please find attached a minimal code
>> example. I do hope I'm sending in the correct format, I'm new to the
>> community.
>>
>> The test creates an integer, robust mutex and condition variable in
>> shared memory. A thread blocks on that condition variable with the
>> associated mutex. After one second, the main thread cancels the blocking
>> thread.
>>
>> I compile as follows:
>>
>> gcc robust_test.c -lpthread -lrt -o robust_test
>>
>> and run
>>
>> ./robust_test
>>
>> On linux it gives the following output:
>> [dstaesse@phoneutria]$ ./robust_test
>> Initializing...
>> Starting thread...
>> Sleeping for one second...
>> Thread started...
>> Cancelling thread...
>> Thread finished.
>> Bye.
>>
>> On FreeBSD I get the following:
>> $ ./robust_test
>> Initializing...
>> Starting thread...
>> Sleeping for one second...
>> Thread started...
>> Cancelling thread...
>> Fatal error 'inact_mtx enter' at line 188 in file
>> /usr/src/lib/libthr/thread/thr_mutex.c (errno = 0)
>> Abort trap (core dumped)
> Try this patch. It worked for me.
> It is enough to patch and then rebuild only libthr:
> cd /usr/src
> patch -p1 <patch
> (cd lib/libthr && make WITHOUT_TESTS=yes all install)
>
> diff --git a/lib/libthr/thread/thr_cond.c b/lib/libthr/thread/thr_cond.c
> index 506b8eca9e7..64d075ca06f 100644
> --- a/lib/libthr/thread/thr_cond.c
> +++ b/lib/libthr/thread/thr_cond.c
> @@ -224,16 +224,26 @@ cond_wait_kernel(struct pthread_cond *cvp, struct pthread_mutex *mp,
> * state and unlock the mutex without making the state
> * consistent and the state will be unrecoverable.
> */
> - if (error2 == 0 && cancel)
> + if (error2 == 0 && cancel) {
> + if (robust) {
> + _mutex_leave_robust(curthread, mp);
> + robust = false;
> + }
> _thr_testcancel(curthread);
> + }
>
> if (error == EINTR)
> error = 0;
> } else {
> /* We know that it didn't unlock the mutex. */
> _mutex_cv_attach(mp, recurse);
> - if (cancel)
> + if (cancel) {
> + if (robust) {
> + _mutex_leave_robust(curthread, mp);
> + robust = false;
> + }
> _thr_testcancel(curthread);
> + }
> error2 = 0;
> }
> if (robust)
--
Dimitri Staessens
Ghent University - imec
Dept. of Information Technology (INTEC)
Internet Based Communication Networks and Services
Technologiepark 15
9052 Zwijnaarde
T: +32 9 331 48 70
F: +32 9 331 48 99
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