public inbox for libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Yubin Ruan <ablacktshirt@gmail.com>
Cc: linux-man <linux-man@vger.kernel.org>,
	 "libc-alpha@sourceware.org" <libc-alpha@sourceware.org>
Subject: Re: [PATCTH 0/2] pthread_mutexattr_setrobust() and pthread_mutex_consistent()
Date: Wed, 13 Sep 2017 12:28:00 -0000	[thread overview]
Message-ID: <CAKgNAkh4iAkz8oL70S3dzztF_oZy+fXohS4OZ2nyySAaAMGX3w@mail.gmail.com> (raw)
In-Reply-To: <20170913083446.GA16265@HP.internal.baidu.com>

Hello Yubin,

On 13 September 2017 at 10:34, Yubin Ruan <ablacktshirt@gmail.com> wrote:
> On Tue, Sep 12, 2017 at 02:41:29PM +0200, Michael Kerrisk (man-pages) wrote:
>> Hello Yubin,
>>
>> [...]
>> > +.B PTHREAD_MUTEX_ROBUST
>> > +can be set on a mutex attribute object so that when the owner of the mutex
>> > +dies or when the process containing such a locked mutex performs
>> > +.IR execve (2)
>> > +, any future attempts to call
>> > +.IR pthread_mutex_lock (3)
>> > +on this mutex will suceed and return
>> > +.B EOWNERDEAD
>> > +to indicate that the original owner no longer exists and the mutex is left in
>> > +an inconsistent state.
>> How did you verify the point regarding execve(2)? I don't see this
>> detailed mentioned in the standards or in the glibc source.
>
> Please see below the program I used to verify that. I haven't go into too much
> detail in the POSIX standard, though. I think I must have read it at [1] or
> somewhere else (don't remember...).

Thanks for the details and example program.

So, I see the kernel code that deals with this now: in
fs/exec.c::exec_mmap(), there is a call to mm_release() which in turn
calls exit_robust_list()

So, this detail isn't in POSIX. I think what I will do is move
discussion of that point into the NOTES.

> And also, it is mentioned at [1] that when the process containing such a locked
> mutex unmaps the memory containing the mutex, the mutex is unlocked... I think
> this is trivial so I don't add it.

It also appears not to be true on Linux, at least in some short tests
I just did.[1] See my modified version of your program, below. Also
when looking at the kernel code, I can see no call to mm_release()
that would lead to this behavior.

Cheers,

Michael

[1] And I wonder if the Solaris documentation is even correct, since,
if we are talking about a shared anonymous mapping, the memory would
not be released until *all* processes have unmapped the memory

/************ verify-execve.c *****************/
#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#define MEMSIZE 4096

#define ERROR_ON(func_name) \
    fprintf(stderr, "error: " #func_name ": line[%d]: %s\n", __LINE__,
strerror(errno));

int main(int argc, char *argv[]) {
    struct shm *shm = NULL;
    int ret_code = 0;
    pthread_mutex_t *mutexp = NULL;
    pthread_mutexattr_t attr;
    pid_t pid = 0;

    shm = mmap(NULL, MEMSIZE, PROT_READ | PROT_WRITE,
               MAP_ANONYMOUS | MAP_SHARED,-1, 0);
    if ((void *)-1 == shm) {
        ERROR_ON(shmat);
        return -1;
    }
    memset(shm, 0, sizeof(pthread_mutex_t));

    printf("Successfully attached shared memory, trying to lock\n");

    //initialize the lock
    mutexp = (pthread_mutex_t *)shm;
    pthread_mutexattr_init(&attr);
    pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);
    pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
    pthread_mutex_init(mutexp, &attr);

    pid = fork();
    if (0 == pid) {
        sleep(1);
        printf("Child about to call pthread_mutex-Lock()\n");
        ret_code = pthread_mutex_lock(mutexp);
        if (EOWNERDEAD == ret_code) {
            printf("child see EOWNERDEAD returned. Verification completed\n");
            pthread_mutex_consistent(mutexp);
            pthread_mutex_unlock(mutexp);
            exit(0);
        } else {
            printf("child see [%d] returned\n", ret_code);
            exit(1);
        }
    } else {
        ret_code = pthread_mutex_lock(mutexp);
        if (0 == ret_code) {
            printf("parent successfully acquired the lock\n");
        } else {
            ERROR_ON(pthread_mutex_lock);
            return -1;
        }

        printf("Parent sleeping 3 seconds\n");
        sleep(3);
        if (munmap(shm, MEMSIZE) == -1)
            ERROR_ON(munmap);
        printf("Parent has unmapped the memory\n");
        sleep(1);
        printf("Parent about to exit\n");
        exit(0);
/*
        printf("parent going to execve(/bin/true)\n");
        execl("/bin/true", "true", (char *) NULL);
*/
    }
    return 0;
}

  parent reply	other threads:[~2017-09-13 12:28 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-20  9:43 Yubin Ruan
2017-08-21  2:25 ` Yubin Ruan
2017-08-21  2:31   ` Yubin Ruan
2017-08-22  0:33 ` Michael Kerrisk (man-pages)
2017-08-22  2:19   ` Yubin Ruan
2017-08-26 14:10     ` Yubin Ruan
2017-09-11  1:50       ` Yubin Ruan
2017-09-11 20:35         ` Michael Kerrisk (man-pages)
2017-09-12 12:41       ` Michael Kerrisk (man-pages)
2017-09-13  1:39         ` Yubin Ruan
2017-09-13  4:09           ` Yubin Ruan
2017-09-13 12:28           ` Michael Kerrisk (man-pages) [this message]
2017-09-15  1:34             ` Yubin Ruan
2017-09-13 15:00       ` Michael Kerrisk (man-opages)
2017-09-15  2:49         ` Yubin Ruan
2017-09-15  7:53           ` Michael Kerrisk (man-pages)

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAKgNAkh4iAkz8oL70S3dzztF_oZy+fXohS4OZ2nyySAaAMGX3w@mail.gmail.com \
    --to=mtk.manpages@gmail.com \
    --cc=ablacktshirt@gmail.com \
    --cc=libc-alpha@sourceware.org \
    --cc=linux-man@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).