svn commit: r198590 - head/sys/kern

[Giorgos Keramidas]

> No, this was caused by the r198507 fragment of postsig(), as well as a
> fragment from the trapsignal(), that added the call to kern_sigprocmask()
> instead of direct manipulation of thread signal mask.
>
>> AFAICT, postsig() is called with proc->p_sigacts->ps_mtx locked, so when
>> we are recursing when reschedule_signals() tries to lock it once more.
>
> Yes, the same statement holds for trapsignal().
>
>> Since we are holding the proc lock in kern_sigprocmask(), is it safe to
>> assert that we own ps_mtx, drop it and re-acquire it immediately after
>> calling reschedule_signals()?
>
> No. Most callers of kern_sigprocmask() do not hold curproc->ps_mtx.
> Only postsig() and trapsig() call kern_sigprocmask() with ps_mtx locked,
> so I have to special-case them.
>
> Could you, please, test the following patch ? What application did
> exposed the issue ?

Logging out of GNOME consistently triggers this.  The thread that is
active in kgdb is gnome-session:

(kgdb) info threads
  ...
  138 Thread 100142 (PID=2314: gnome-session)  doadump () at pcpu.h:246
  137 Thread 100100 (PID=2314: gnome-session/initial thread)
        sched_switch (td=0xc6a86230, newtd=0xc6564230, flags=1538)
        at /usr/src/sys/kern/sched_ule.c:1864
  ...

I'll try the patch in a few hours and report back.  Thanks! :)

> diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
> index 7f5cfa3..e174df1 100644
> --- a/sys/kern/kern_sig.c
> +++ b/sys/kern/kern_sig.c
> @@ -220,7 +220,7 @@ static int sigproptbl[NSIG] = {
>          SA_KILL|SA_PROC,		/* SIGUSR2 */
>  };
>
> -static void reschedule_signals(struct proc *p, sigset_t block);
> +static void reschedule_signals(struct proc *p, sigset_t block, int flags);
>
>  static void
>  sigqueue_start(void)
> @@ -1024,7 +1024,7 @@ kern_sigprocmask(struct thread *td, int how, sigset_t *set, sigset_t *oset,
>  	 * possibly waking it up.
>  	 */
>  	if (p->p_numthreads != 1)
> -		reschedule_signals(p, new_block);
> +		reschedule_signals(p, new_block, flags);
>
>  	if (!(flags & SIGPROCMASK_PROC_LOCKED))
>  		PROC_UNLOCK(p);
> @@ -1859,13 +1859,11 @@ trapsignal(struct thread *td, ksiginfo_t *ksi)
>  #endif
>  		(*p->p_sysent->sv_sendsig)(ps->ps_sigact[_SIG_IDX(sig)],
>  				ksi, &td->td_sigmask);
> -		SIGSETOR(td->td_sigmask, ps->ps_catchmask[_SIG_IDX(sig)]);
> -		if (!SIGISMEMBER(ps->ps_signodefer, sig)) {
> -			SIGEMPTYSET(mask);
> +		mask = ps->ps_catchmask[_SIG_IDX(sig)];
> +		if (!SIGISMEMBER(ps->ps_signodefer, sig))
>  			SIGADDSET(mask, sig);
> -			kern_sigprocmask(td, SIG_BLOCK, &mask, NULL,
> -			    SIGPROCMASK_PROC_LOCKED);
> -		}
> +		kern_sigprocmask(td, SIG_BLOCK, &mask, NULL,
> +		    SIGPROCMASK_PROC_LOCKED | SIGPROCMASK_PS_LOCKED);
>  		if (SIGISMEMBER(ps->ps_sigreset, sig)) {
>  			/*
>  			 * See kern_sigaction() for origin of this code.
> @@ -2401,7 +2399,7 @@ stopme:
>  }
>
>  static void
> -reschedule_signals(struct proc *p, sigset_t block)
> +reschedule_signals(struct proc *p, sigset_t block, int flags)
>  {
>  	struct sigacts *ps;
>  	struct thread *td;
> @@ -2419,12 +2417,14 @@ reschedule_signals(struct proc *p, sigset_t block)
>
>  		td = sigtd(p, i, 0);
>  		signotify(td);
> -		mtx_lock(&ps->ps_mtx);
> +		if (!(flags & SIGPROCMASK_PS_LOCKED))
> +			mtx_lock(&ps->ps_mtx);
>  		if (p->p_flag & P_TRACED || SIGISMEMBER(ps->ps_sigcatch, i))
>  			tdsigwakeup(td, i, SIG_CATCH,
>  			    (SIGISMEMBER(ps->ps_sigintr, i) ? EINTR :
>  			     ERESTART));
> -		mtx_unlock(&ps->ps_mtx);
> +		if (!(flags & SIGPROCMASK_PS_LOCKED))
> +			mtx_unlock(&ps->ps_mtx);
>  	}
>  }
>
> @@ -2452,7 +2452,7 @@ tdsigcleanup(struct thread *td)
>  	SIGFILLSET(unblocked);
>  	SIGSETNAND(unblocked, td->td_sigmask);
>  	SIGFILLSET(td->td_sigmask);
> -	reschedule_signals(p, unblocked);
> +	reschedule_signals(p, unblocked, 0);
>
>  }
>
> @@ -2734,15 +2734,11 @@ postsig(sig)
>  		} else
>  			returnmask = td->td_sigmask;
>
> -		kern_sigprocmask(td, SIG_BLOCK,
> -		    &ps->ps_catchmask[_SIG_IDX(sig)], NULL,
> -		    SIGPROCMASK_PROC_LOCKED);
> -		if (!SIGISMEMBER(ps->ps_signodefer, sig)) {
> -			SIGEMPTYSET(mask);
> +		mask = ps->ps_catchmask[_SIG_IDX(sig)];
> +		if (!SIGISMEMBER(ps->ps_signodefer, sig))
>  			SIGADDSET(mask, sig);
> -			kern_sigprocmask(td, SIG_BLOCK, &mask, NULL,
> -			    SIGPROCMASK_PROC_LOCKED);
> -		}
> +		kern_sigprocmask(td, SIG_BLOCK, &mask, NULL,
> +		    SIGPROCMASK_PROC_LOCKED | SIGPROCMASK_PS_LOCKED);
>
>  		if (SIGISMEMBER(ps->ps_sigreset, sig)) {
>  			/*
> diff --git a/sys/sys/signalvar.h b/sys/sys/signalvar.h
> index b9a54f0..c27a128 100644
> --- a/sys/sys/signalvar.h
> +++ b/sys/sys/signalvar.h
> @@ -319,6 +319,7 @@ extern int kern_logsigexit;	/* Sysctl variable kern.logsigexit */
>  /* flags for kern_sigprocmask */
>  #define	SIGPROCMASK_OLD		0x0001
>  #define	SIGPROCMASK_PROC_LOCKED	0x0002
> +#define	SIGPROCMASK_PS_LOCKED	0x0004
>
>  /*
>   * Machine-independent functions:
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