Messages in this thread | | | Date | Mon, 18 May 2015 10:20:37 -0400 | From | Don Zickus <> | Subject | Re: suspend regression in 4.1-rc1 |
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On Mon, May 18, 2015 at 11:31:50AM +0200, Peter Zijlstra wrote: > On Mon, May 18, 2015 at 11:03:37AM +0200, Michal Hocko wrote: > > This doesn't hang anymore. I've just had to move the mutex definition > > up to make it compile. So feel free to add my > > I've also fixed a lock leak, see goto unlock :-) > > > Reported-and-tested-by: Michal Hocko <mhocko@suse.cz> > > *blink* that actually fixed it.. > > That somewhat leaves me at a loss explaining how s2r was failing. > > --- > Subject: watchdog: Fix merge 'conflict' > > Two watchdog changes that came through different trees had a non > conflicting conflict, that is, one changed the semantics of a variable > but no actual code conflict happened. So the merge appeared fine, but > the resulting code did not behave as expected. > > Commit 195daf665a62 ("watchdog: enable the new user interface of the > watchdog mechanism") changes the semantics of watchdog_user_enabled, > which thereafter is only used by the functions introduced by > b3738d293233 ("watchdog: Add watchdog enable/disable all functions"). > > There further appears to be a distinct lack of serialization between > setting and using watchdog_enabled, so perhaps we should wrap the > {en,dis}able_all() things in watchdog_proc_mutex. > > This patch fixes a s2r failure reported by Michal; which I cannot > readily explain. But this does make the code internally consistent > again.
I agree with Peter's locking approach. We need to do better locking the variables here. Poking around the code I see too many variables being exposed sadly.
Thanks Peter!
Andrew, this patch can replace 'watchdog-fix-watchdog_nmi_enable_all.patch' on your queue.
Acked-by: Don Zickus <dzickus@redhat.com> > > Reported-and-tested-by: Michal Hocko <mhocko@suse.cz> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/watchdog.c | 20 +++++++++++++++----- > 1 file changed, 15 insertions(+), 5 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 2316f50..506edcc5 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -41,6 +41,8 @@ > #define NMI_WATCHDOG_ENABLED (1 << NMI_WATCHDOG_ENABLED_BIT) > #define SOFT_WATCHDOG_ENABLED (1 << SOFT_WATCHDOG_ENABLED_BIT) > > +static DEFINE_MUTEX(watchdog_proc_mutex); > + > #ifdef CONFIG_HARDLOCKUP_DETECTOR > static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED; > #else > @@ -608,26 +610,36 @@ void watchdog_nmi_enable_all(void) > { > int cpu; > > - if (!watchdog_user_enabled) > - return; > + mutex_lock(&watchdog_proc_mutex); > + > + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) > + goto unlock; > > get_online_cpus(); > for_each_online_cpu(cpu) > watchdog_nmi_enable(cpu); > put_online_cpus(); > + > +unlock: > + mutex_lock(&watchdog_proc_mutex); > } > > void watchdog_nmi_disable_all(void) > { > int cpu; > > + mutex_lock(&watchdog_proc_mutex); > + > if (!watchdog_running) > - return; > + goto unlock; > > get_online_cpus(); > for_each_online_cpu(cpu) > watchdog_nmi_disable(cpu); > put_online_cpus(); > + > +unlock: > + mutex_unlock(&watchdog_proc_mutex); > } > #else > static int watchdog_nmi_enable(unsigned int cpu) { return 0; } > @@ -744,8 +756,6 @@ static int proc_watchdog_update(void) > > } > > -static DEFINE_MUTEX(watchdog_proc_mutex); > - > /* > * common function for watchdog, nmi_watchdog and soft_watchdog parameter > *
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