signalfd() not handling sigqueue() sigval data correctly - Kernel

This is a discussion on signalfd() not handling sigqueue() sigval data correctly - Kernel ; Hi Davide, I was doing some playing about with signalfd(), and seem to have encountered a bug: when a signalfd read() fetches data for a signal that was sent by sigqueue(), the data accompanying the signal is not returned. Instead ...

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Thread: signalfd() not handling sigqueue() sigval data correctly

  1. signalfd() not handling sigqueue() sigval data correctly

    Hi Davide,

    I was doing some playing about with signalfd(), and seem to have encountered a
    bug: when a signalfd read() fetches data for a signal that was sent by
    sigqueue(), the data accompanying the signal is not returned. Instead
    ssi_int/ssi_ptr is zero.

    I've not looked into the cause of the problem, but the programs below can be
    used to demonstrate it.

    Here's an example run:

    # Run in the background, waiting for signal 44.
    $ ./signalfd_sigval 44 &
    ../signalfd_sigval: PID = 14783
    [1] 14783
    # Send signal 44 to PID 14783 with accompanying data 123
    $ ./sigqueue 14783 44 123
    /home/mtk/alp/signals/sigqueue: PID = 14784
    Got signal 44
    ssi_code= -1
    ssi_pid = 14784
    ssi_uid = 1000
    ssi_int = 0 <= should be 123 here
    ssi_ptr = 0 <= and here the hex version of 123

    Could you take a look at this?

    Cheers,

    Michael


    /* signalfd_sigval.c */

    #define _GNU_SOURCE
    #include
    #include
    #include
    #include
    #if defined(__i386__)
    #define __NR_signalfd 321
    #endif

    struct signalfd_siginfo {
    uint32_t ssi_signo;
    int32_t ssi_errno;
    int32_t ssi_code;
    uint32_t ssi_pid;
    uint32_t ssi_uid;
    int32_t ssi_fd;
    uint32_t ssi_tid;
    uint32_t ssi_band;
    uint32_t ssi_overrun;
    uint32_t ssi_trapno;
    int32_t ssi_status;
    int32_t ssi_int;
    uint64_t ssi_ptr;
    uint64_t ssi_utime;
    uint64_t ssi_stime;
    uint64_t ssi_addr;
    uint8_t __pad[48];
    };

    static int
    signalfd(int ufd, sigset_t const *mask)
    {
    #define SIZEOF_SIG (_NSIG / 8)
    #define SIZEOF_SIGSET (SIZEOF_SIG > sizeof(sigset_t) ? \
    sizeof(sigset_t): SIZEOF_SIG)
    return syscall(__NR_signalfd, ufd, mask, SIZEOF_SIGSET);
    }

    // #include
    #include
    #include
    #include
    #include

    #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)

    int
    main(int argc, char *argv[])
    {
    sigset_t mask;
    int sfd;
    struct signalfd_siginfo fdsi;
    ssize_t s;

    if (argc != 2) {
    fprintf(stderr, "Usage: %s sig-num\n", argv[0]);
    exit(EXIT_FAILURE);
    }

    printf("%s: PID = %ld\n", argv[0], (long) getpid());

    sigemptyset(&mask);
    sigaddset(&mask, atoi(argv[1]));

    if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)
    errExit("sigprocmask");

    sfd = signalfd(-1, &mask);
    if (sfd == -1)
    errExit("signalfd");

    for (; {
    s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
    if (s != sizeof(struct signalfd_siginfo))
    errExit("read");

    printf("Got signal %d\n", fdsi.ssi_signo);
    printf(" ssi_code= %d\n", fdsi.ssi_code);
    printf(" ssi_pid = %d\n", fdsi.ssi_pid);
    printf(" ssi_uid = %d\n", fdsi.ssi_uid);
    printf(" ssi_int = %d\n", fdsi.ssi_int);
    printf(" ssi_ptr = %llx\n", fdsi.ssi_ptr);
    }
    }



    /* sigqueue.c */

    #include
    #include
    #include
    #include
    #include

    #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
    } while (0)

    int
    main(int argc, char *argv[])
    {
    union sigval sv;

    if (argc != 4) {
    fprintf(stderr, "Usage: %s pid sig-num data\n", argv[0]);
    exit(EXIT_FAILURE);
    }

    printf("%s: PID = %ld\n", argv[0], (long) getpid());

    sv.sival_int = atoi(argv[3]);
    if (sigqueue(atoi(argv[1]), atoi(argv[2]), sv) == -1)
    errExit("sigqueue");

    exit(EXIT_SUCCESS);
    }

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  2. Re: signalfd() not handling sigqueue() sigval data correctly

    On Tue, 8 Apr 2008, Michael Kerrisk wrote:

    > Hi Davide,
    >
    > I was doing some playing about with signalfd(), and seem to have encountered a
    > bug: when a signalfd read() fetches data for a signal that was sent by
    > sigqueue(), the data accompanying the signal is not returned. Instead
    > ssi_int/ssi_ptr is zero.


    Are you able to fetch those info with, say, sigtimedwait(2)?



    - Davide


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  3. Re: signalfd() not handling sigqueue() sigval data correctly

    On Wed, Apr 9, 2008 at 1:37 AM, Davide Libenzi wrote:
    > On Tue, 8 Apr 2008, Michael Kerrisk wrote:
    >
    > > Hi Davide,
    > >
    > > I was doing some playing about with signalfd(), and seem to have encountered a
    > > bug: when a signalfd read() fetches data for a signal that was sent by
    > > sigqueue(), the data accompanying the signal is not returned. Instead
    > > ssi_int/ssi_ptr is zero.

    >
    > Are you able to fetch those info with, say, sigtimedwait(2)?


    Yes.


    --
    Michael Kerrisk
    Maintainer of the Linux man-pages project
    http://www.kernel.org/doc/man-pages/
    Want to report a man-pages bug? Look here:
    http://www.kernel.org/doc/man-pages/reporting_bugs.html
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  4. Re: signalfd() not handling sigqueue() sigval data correctly

    On Wed, 9 Apr 2008, Michael Kerrisk wrote:

    > On Wed, Apr 9, 2008 at 1:37 AM, Davide Libenzi wrote:
    > > On Tue, 8 Apr 2008, Michael Kerrisk wrote:
    > >
    > > > Hi Davide,
    > > >
    > > > I was doing some playing about with signalfd(), and seem to have encountered a
    > > > bug: when a signalfd read() fetches data for a signal that was sent by
    > > > sigqueue(), the data accompanying the signal is not returned. Instead
    > > > ssi_int/ssi_ptr is zero.

    > >
    > > Are you able to fetch those info with, say, sigtimedwait(2)?

    >
    > Yes.


    Okie, found it. Tomorrow I'll post a patch. Thank you for reporting.



    - Davide


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  5. Re: signalfd() not handling sigqueue() sigval data correctly

    On Tue, 8 Apr 2008, Michael Kerrisk wrote:

    > Hi Davide,
    >
    > I was doing some playing about with signalfd(), and seem to have encountered a
    > bug: when a signalfd read() fetches data for a signal that was sent by
    > sigqueue(), the data accompanying the signal is not returned. Instead
    > ssi_int/ssi_ptr is zero.


    Michael, can you give the patch below a spin? I tested it on my x86_64 box
    and seems to be working fine:

    Got signal 44
    ssi_code= -1
    ssi_pid = 6314
    ssi_uid = 1000
    ssi_int = 123
    ssi_ptr = 7b




    - Davide


    ---
    fs/signalfd.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    Index: linux-2.6.mod/fs/signalfd.c
    ================================================== =================
    --- linux-2.6.mod.orig/fs/signalfd.c 2008-04-09 11:53:37.000000000 -0700
    +++ linux-2.6.mod/fs/signalfd.c 2008-04-09 12:05:46.000000000 -0700
    @@ -111,9 +111,14 @@
    err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    break;
    - default: /* this is just in case for now ... */
    + default:
    + /*
    + * This case catches also the signals queued by sigqueue().
    + */
    err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
    err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    + err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    + err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
    break;
    }

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  6. Re: signalfd() not handling sigqueue() sigval data correctly

    Hi Davide,

    > > I was doing some playing about with signalfd(), and seem to have encountered a
    > > bug: when a signalfd read() fetches data for a signal that was sent by
    > > sigqueue(), the data accompanying the signal is not returned. Instead
    > > ssi_int/ssi_ptr is zero.

    >
    > Michael, can you give the patch below a spin? I tested it on my x86_64 box
    > and seems to be working fine:
    >
    > Got signal 44
    > ssi_code= -1
    > ssi_pid = 6314
    > ssi_uid = 1000
    > ssi_int = 123
    > ssi_ptr = 7b


    This works for me on x86-32. Thanks Davide!

    Cheers,

    Michael

    > ---
    > fs/signalfd.c | 7 ++++++-
    > 1 file changed, 6 insertions(+), 1 deletion(-)
    >
    > Index: linux-2.6.mod/fs/signalfd.c
    > ================================================== =================
    > --- linux-2.6.mod.orig/fs/signalfd.c 2008-04-09 11:53:37.000000000 -0700
    > +++ linux-2.6.mod/fs/signalfd.c 2008-04-09 12:05:46.000000000 -0700
    > @@ -111,9 +111,14 @@
    > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    > break;
    > - default: /* this is just in case for now ... */
    > + default:
    > + /*
    > + * This case catches also the signals queued by sigqueue().
    > + */
    > err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
    > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    > + err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
    > break;
    > }
    >
    >




    --
    Michael Kerrisk
    Maintainer of the Linux man-pages project: http://www.kernel.org/doc/man-pages/
    Want to report a man-pages bug? Look here:
    http://www.kernel.org/doc/man-pages/reporting_bugs.html
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  7. Re: signalfd() not handling sigqueue() sigval data correctly

    On Thu, Apr 10, 2008 at 7:03 AM, Michael Kerrisk
    wrote:
    > Hi Davide,
    >
    > > > I was doing some playing about with signalfd(), and seem to have encountered a
    > > > bug: when a signalfd read() fetches data for a signal that was sent by
    > > > sigqueue(), the data accompanying the signal is not returned. Instead
    > > > ssi_int/ssi_ptr is zero.

    > >
    > > Michael, can you give the patch below a spin? I tested it on my x86_64 box
    > > and seems to be working fine:
    > >
    > > Got signal 44
    > > ssi_code= -1
    > > ssi_pid = 6314
    > > ssi_uid = 1000
    > > ssi_int = 123
    > > ssi_ptr = 7b

    >
    > This works for me on x86-32. Thanks Davide!


    Davide,

    Are you going to get this pushed into 2.6.26? I assume we can't get
    it into 2.6.25...

    Cheers,

    Michael

    > > ---
    > > fs/signalfd.c | 7 ++++++-
    > > 1 file changed, 6 insertions(+), 1 deletion(-)
    > >
    > > Index: linux-2.6.mod/fs/signalfd.c
    > > ================================================== =================
    > > --- linux-2.6.mod.orig/fs/signalfd.c 2008-04-09 11:53:37.000000000 -0700
    > > +++ linux-2.6.mod/fs/signalfd.c 2008-04-09 12:05:46.000000000 -0700
    > > @@ -111,9 +111,14 @@
    > > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    > > err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    > > break;
    > > - default: /* this is just in case for now ... */
    > > + default:
    > > + /*
    > > + * This case catches also the signals queued by sigqueue().
    > > + */
    > > err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
    > > err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
    > > + err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
    > > + err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
    > > break;
    > > }
    > >
    > >

    >
    >
    >
    >
    > --
    > Michael Kerrisk
    > Maintainer of the Linux man-pages project: http://www.kernel.org/doc/man-pages/
    > Want to report a man-pages bug? Look here:
    > http://www.kernel.org/doc/man-pages/reporting_bugs.html
    >




    --
    Michael Kerrisk
    Maintainer of the Linux man-pages project
    http://www.kernel.org/doc/man-pages/
    Want to report a man-pages bug? Look here:
    http://www.kernel.org/doc/man-pages/reporting_bugs.html
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  8. Re: signalfd() not handling sigqueue() sigval data correctly

    On Thu, 10 Apr 2008, Michael Kerrisk wrote:

    > On Thu, Apr 10, 2008 at 7:03 AM, Michael Kerrisk
    > wrote:
    > > Hi Davide,
    > >
    > > > > I was doing some playing about with signalfd(), and seem to have encountered a
    > > > > bug: when a signalfd read() fetches data for a signal that was sent by
    > > > > sigqueue(), the data accompanying the signal is not returned. Instead
    > > > > ssi_int/ssi_ptr is zero.
    > > >
    > > > Michael, can you give the patch below a spin? I tested it on my x86_64 box
    > > > and seems to be working fine:
    > > >
    > > > Got signal 44
    > > > ssi_code= -1
    > > > ssi_pid = 6314
    > > > ssi_uid = 1000
    > > > ssi_int = 123
    > > > ssi_ptr = 7b

    > >
    > > This works for me on x86-32. Thanks Davide!

    >
    > Davide,
    >
    > Are you going to get this pushed into 2.6.26? I assume we can't get
    > it into 2.6.25...


    I'll be sending it Andrew-bound today. I dunno where it'll land mainline.


    - Davide


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