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    SubjectRe: situation with signals
    On 10/27/2010 5:37 PM, Al Viro wrote:
    > On Wed, Oct 27, 2010 at 05:02:10PM -0400, Chris Metcalf wrote
    >> I set aside this thread to look at when I had a minute, and I believe there
    >> is just one of the signal issues present in the tile code. The fix is to
    >> reset regs->fault to something other than the "syscall" fault type when
    >> exiting from do_signal(), so I'll submit that up for 2.6.37 shortly.
    > FWIW, I'd do that in handle_signal() when hitting a syscall restart.

    Right now I'm just doing it unconditionally in handle_signal()'s caller
    whether or not I actually call handle_signal, to be paranoid:

    @@ -353,11 +353,11 @@
    * clear the TS_RESTORE_SIGMASK flag.
    */
    current_thread_info()->status &= ~TS_RESTORE_SIGMASK;
    }

    - return;
    + goto done;
    }

    /* Did we come from a system call? */
    if (regs->faultnum == INT_SWINT_1) {
    /* Restart the system call - no handlers present */
    @@ -381,10 +381,14 @@
    /* If there's no signal to deliver, just put the saved sigmask back. */
    if (current_thread_info()->status & TS_RESTORE_SIGMASK) {
    current_thread_info()->status &= ~TS_RESTORE_SIGMASK;
    sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
    }
    +
    +done:
    + /* Avoid double syscall restart if there are nested signals. */
    + regs->faultnum = INT_SWINT_1_SIGRETURN;
    }


    > BTW, is everything in your pt_regs safe to modify?

    What an interesting observation. :-) In fact, it would be possible to
    overwrite the privilege level (the ex1 register) from within the signal
    handler and then return to run arbitrary code at kernel PL. I'll fix it.

    --
    Chris Metcalf, Tilera Corp.
    http://www.tilera.com


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