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SubjectRe: [BUG, TEST PATCH] stallout race between SIGCONT and SIGSTOP
On 09/24, Joe Korty wrote:
> On Wed, Sep 24, 2008 at 11:05:41AM -0400, Oleg Nesterov wrote:
> > Joe says:
> >> So it looks like the test is in error, not the kernel.
> >
> > and I am happy to agree.
> > I think sigaction/10-1.c should be fixed, please see the patch below.
> A year or two ago I sent to Intel some OpenPosixTestSuite fixes, and they
> were accepted. Send it in (to the people listed in the comments at the
> front of the .c file), hopefully they are still at Intel.

OK, thanks, will do.

> > I did the test patch to be sure:
> >
> > --- 26-rc2/kernel/signal.c~ 2008-09-20 20:37:52.000000000 +0400
> > +++ 26-rc2/kernel/signal.c 2008-09-24 18:43:34.000000000 +0400
> > @@ -808,7 +808,7 @@ static int send_signal(int sig, struct s
> > * exactly one non-rt signal, so that we can get more
> > * detailed information about the cause of the signal.
> > */
> > - if (legacy_queue(pending, sig))
> > + if (sig != SIGCHLD && legacy_queue(pending, sig))
> > return 0;
> > /*
> > * fast-pathed signals for kernel-internal things like SIGSTOP
> >
> > and now your test-case doesn't hang.
> Very interesting! I am not sure this is Posix conformant,

No, no, the patch is of course wrong, I did it only to check my

> as Posix
> seems to say that posting a SIGSTOP or SIGCHLD clears out all pending

Hmm. Are you sure?

Anyway, this is not what Linux does. If a non-rt signal is pending, the
next signal with the same number is silently ignored. SIGCHLD too.

> Still it might be workable

Confused. Do you agree the kernel is not buggy?

To clarify, none of SIGCONTs/SIGSTOPs is lost. But the test-case assumes
that it must always receive SIGCHLD + CLD_STOPPED. This is not true because
SIGCHLD is not queueable, and we have another "stream" of SIGCHLDs which

For example, the "opposite" code


was always wrong, but


happened to work before that commit. But please note that it is wrong
anyway. For example, if we have another sub-thread, we can miss
CLD_STOPPED even without the commit which changed the timing.


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