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Date: Fri, 7 Dec 2018 10:44:20 -0500
From: Rich Felker <dalias@...c.org>
To: Arkadiusz Sienkiewicz <sienkiewiczarkadiusz@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: aio_cancel segmentation fault for in progress write
requests
On Fri, Dec 07, 2018 at 01:52:31PM +0100, Arkadiusz Sienkiewicz wrote:
> Hi,
>
> I'm experiencing segmentation fault when I invoke aio_cancel on request
> which is in EINPROGRESS state. This happens only with libc muls (used
> version - 1.1.12-r8) and only on one (dual Intel Xeon Gold 6128) of few
> computers I've tried it on - please let me know if you need more
> information about that machine. Attached is very simple program
> (aioWrite.cpp) that reproduces this problem.
>
> alpine-tmp-0:~$ ./aioWrite
> Segmentation fault (core dumped)
>
> Bt from gdb shows problem is in aio_cancel.
This is not correct:
>
> (gdb) r
> Starting program: ~/aioWrite
> [New LWP 70321]
>
> Program received signal ?, Unknown signal.
> [Switching to LWP 70321]
This just shows that the aio thread received the cancellation request.
It's not a crash or a problem. However, gdb's reporting of it as
"Unknown signal" and inability to pass it on correctly indicates that
something is wrong with the gdb on your system. I've hit this issue a
lot but it works on some systems and I don't recall what the
cause/difference behind it is. We should work to figure that out and
get an appropriate fix in distros that are affected.
> #include <stdio.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <string.h>
> #include <errno.h>
> #include <stdlib.h>
> #include <aio.h>
>
> #define TNAME "aio_write/1-1.c"
>
> int main() {
> char tmpfname[256];
> #define BUF_SIZE 512512
> char buf[BUF_SIZE];
> char check[BUF_SIZE+1];
> int fd;
> struct aiocb aiocb;
> int err;
> int ret;
>
> snprintf(tmpfname, sizeof(tmpfname), "pts_aio_write_1_1_%d", getpid());
> unlink(tmpfname);
> fd = open(tmpfname, O_CREAT | O_RDWR | O_EXCL, S_IRUSR | S_IWUSR);
> if (fd == -1) {
> printf(TNAME " Error at open(): %s\n", strerror(errno));
> exit(1);
> }
>
> unlink(tmpfname);
>
> memset(buf, 0xaa, BUF_SIZE);
> memset(&aiocb, 0, sizeof(struct aiocb));
> aiocb.aio_fildes = fd;
> aiocb.aio_buf = buf;
> aiocb.aio_nbytes = BUF_SIZE;
>
> if (aio_write(&aiocb) == -1) {
> printf(TNAME " Error at aio_write(): %s\n", strerror(errno));
> close(fd);
> exit(2);
> }
>
> int cancellationStatus = aio_cancel(fd, &aiocb);
> printf (TNAME " cancelationStatus : %d\n", cancellationStatus);
>
> /* Wait until completion */
> while (aio_error (&aiocb) == EINPROGRESS);
>
> close(fd);
> printf ("Test PASSED\n");
> return 0;
> }
I just tried this test and it works for me on 32-bit x86. I'll try
some other systems and see if I can reproduce the issue. It could be a
bug in the test but I didn't see anything obviously wrong with it.
Rich
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