From: Takashi Yano <takashi.yano@nifty.ne.jp>
To: cygwin-developers@cygwin.com
Subject: Re: deadlock on console mutex in gdb
Date: Thu, 13 Jan 2022 20:09:52 +0900 [thread overview]
Message-ID: <20220113200952.fe8c3b10fe0efda02a68c7e8@nifty.ne.jp> (raw)
In-Reply-To: <vritczlnxgqt.fsf@gmail.com>
On Thu, 23 Dec 2021 15:28:58 -0400
David McFarland wrote:
> I've also been hitting another console related deadlock, even when
> there's no debugger involved:
[...]
> I can use this program:
>
> =====test-pt.c
> #include <pthread.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <stdlib.h>
>
> void *thread(void* p) {
> for (int i = 0;; ++i) {
> int fd = posix_openpt(O_RDWR | O_NOCTTY);
> close(fd);
> fprintf(stderr, "test %i\n", i);
> }
> return 0;
> }
>
> int main() {
> pthread_t ids[3];
> for (int i = 0; i < 3; ++i) {
> pthread_create(&ids[i], 0, &thread, &ids[i]);
> }
> for (int i = 0; i < 3; ++i) {
> pthread_join(ids[i], 0);
> }
> return 0;
> }
> =====
>
> compiled with:
>
> $ gcc -D_GNU_SOURCE test-pt.c -o test-pt
>
> To hit those asserts.
Thanks for the report. I tried your test case, however I
encountered another problem of pty. The test case causes
memory leak and exhausts the system memory in a short time.
I will submit a patch for the memory leak issue.
> Perhaps the mutex should never be closed? It's also worrying that
> acquiring the mutex just silently fails before a PT is opened.
> There could be a thread that is acting as if it has a lock a the time
> that the mutex is created, and it will even try to release the lock.
>
> It might just be safest to create it at process start, but it could have
> a significant performance cost.
With the patch above, I tried your test case again and
confirmed the assertion fails indeed. I also confirmed
the deadlock.
Thanks for pointing out this. Let me consider.
--
Takashi Yano <takashi.yano@nifty.ne.jp>
next prev parent reply other threads:[~2022-01-13 11:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-22 15:26 David McFarland
2021-12-22 20:44 ` Takashi Yano
2021-12-22 22:17 ` David McFarland
2021-12-23 9:24 ` Takashi Yano
2021-12-23 15:32 ` David McFarland
2021-12-23 19:28 ` David McFarland
2021-12-26 15:25 ` David McFarland
2022-01-13 11:09 ` Takashi Yano [this message]
2022-01-13 10:56 ` Takashi Yano
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