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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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