Messages in this thread | | | Date | Thu, 12 Mar 2009 15:17:43 -0700 | From | Darren Hart <> | Subject | Re: [PATCH 5/6] futex: unlock before returning -EFAULT |
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Peter Zijlstra wrote: > On Thu, 2009-03-12 at 00:56 -0700, Darren Hart wrote: >> futex_lock_pi can potentially return -EFAULT with the rt_mutex held. This >> seems like the wrong thing to do as userspace should assume -EFAULT means the >> lock was not taken. Even if it could figure this out, we'd be leaving the >> pi_state->owner in an inconsistent state. This patch unlocks the rt_mutex >> prior to returning -EFAULT to userspace. > > lockdep would complain, one is not to leave the kernel with locks held. > >> Build and boot tested on a 4 way Intel x86_64 workstation. Passes basic >> pthread_mutex and PI tests out of ltp/testcases/realtime. > > You keep mentioning these tests.. makes me wonder how much of the futex > code paths they actually test. Got any coverage info on them?
Right now these are tests I know the most about and I know they excercise the futex_wait, futex_wake, futex_(un)lock_pi, and futex_requeue paths via the pthread_mutex* and pthread_cond* APIs. I doubt they test the fault logic very well, and I know they don't test shared futexes.
I'd really like to ramp up my efforts on the raw sys_futex tests I've been working on, but just haven't had the cycles. I suspect they will become necessary for requeue_pi however. I also think we should look at some kind of futex-debug.c infrastructure that also adds some fault-injection to test the various error paths.
-- Darren
> >> Signed-off-by: Darren Hart <dvhltc@us.ibm.com> >> Cc: Thomas Gleixner <tglx@linutronix.de> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Ingo Molnar <mingo@elte.hu> >> Cc: Rusty Russell <rusty@rustcorp.com.au> >> --- >> >> kernel/futex.c | 7 +++++++ >> 1 files changed, 7 insertions(+), 0 deletions(-) >> >> diff --git a/kernel/futex.c b/kernel/futex.c >> index 6579912..c980a55 100644 >> --- a/kernel/futex.c >> +++ b/kernel/futex.c >> @@ -1567,6 +1567,13 @@ retry_locked: >> } >> } >> >> + /* >> + * If fixup_pi_state_owner() faulted and was unable to handle the >> + * fault, unlock it and return the fault to userspace. >> + */ >> + if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) >> + rt_mutex_unlock(&q.pi_state->pi_mutex); >> + >> /* Unqueue and drop the lock */ >> unqueue_me_pi(&q); >> >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team
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