| Message ID | 20200907041528.12540-2-matthew.ruffell@canonical.com |
|---|---|
| State | New |
| Headers | show |
| Series | clock: overriding the clocksource should select the requested clocksource | expand |
On 07.09.20 06:15, Matthew Ruffell wrote: > From: Kyle Walker <kwalker@redhat.com> > > BugLink: https://bugs.launchpad.net/bugs/1894591 > > Clocksources don't get the VALID_FOR_HRES flag until they have been > checked by a watchdog. However, when using an override, the > clocksource_select logic will clear the override value if the > clocksource is not marked VALID_FOR_HRES during that inititial check. > When using the boot arguments clocksource=<foo>, this selection can > run before the watchdog, and can cause the override to be incorrectly > cleared. > > To address this condition, the override_name is only invalidated for > unstable clocksources. Otherwise, the override is left intact until after > the watchdog has validated the clocksource as stable/unstable. > > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Richard Cochran <richardcochran@gmail.com> > Cc: Prarit Bhargava <prarit@redhat.com> > Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> > Signed-off-by: Kyle Walker <kwalker@redhat.com> > Signed-off-by: John Stultz <john.stultz@linaro.org> > (cherry picked from commit 36374583f9084cdab4b5dcf5521a3ce55bebb9fa) > Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com> Clean cherry-pick and positive test result. Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com> Thanks. > --- > kernel/time/clocksource.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index a20368e1a720..ac4c84361be0 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -607,9 +607,18 @@ static void __clocksource_select(bool skipcur) > */ > if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { > /* Override clocksource cannot be used. */ > - pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n", > - cs->name); > - override_name[0] = 0; > + if (cs->flags & CLOCK_SOURCE_UNSTABLE) { > + pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", > + cs->name); > + override_name[0] = 0; > + } else { > + /* > + * The override cannot be currently verified. > + * Deferring to let the watchdog check. > + */ > + pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", > + cs->name); > + } > } else > /* Override clocksource can be used. */ > best = cs; >
On Mon, Sep 07, 2020 at 04:15:28PM +1200, Matthew Ruffell wrote: > From: Kyle Walker <kwalker@redhat.com> > > BugLink: https://bugs.launchpad.net/bugs/1894591 > > Clocksources don't get the VALID_FOR_HRES flag until they have been > checked by a watchdog. However, when using an override, the > clocksource_select logic will clear the override value if the > clocksource is not marked VALID_FOR_HRES during that inititial check. > When using the boot arguments clocksource=<foo>, this selection can > run before the watchdog, and can cause the override to be incorrectly > cleared. > > To address this condition, the override_name is only invalidated for > unstable clocksources. Otherwise, the override is left intact until after > the watchdog has validated the clocksource as stable/unstable. > > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Richard Cochran <richardcochran@gmail.com> > Cc: Prarit Bhargava <prarit@redhat.com> > Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> > Signed-off-by: Kyle Walker <kwalker@redhat.com> > Signed-off-by: John Stultz <john.stultz@linaro.org> > (cherry picked from commit 36374583f9084cdab4b5dcf5521a3ce55bebb9fa) > Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com> > --- > kernel/time/clocksource.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index a20368e1a720..ac4c84361be0 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -607,9 +607,18 @@ static void __clocksource_select(bool skipcur) > */ > if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { > /* Override clocksource cannot be used. */ > - pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n", > - cs->name); > - override_name[0] = 0; > + if (cs->flags & CLOCK_SOURCE_UNSTABLE) { > + pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", > + cs->name); > + override_name[0] = 0; > + } else { > + /* > + * The override cannot be currently verified. > + * Deferring to let the watchdog check. > + */ > + pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", > + cs->name); > + } > } else > /* Override clocksource can be used. */ > best = cs; > -- > 2.25.1 Acked-by: William Breathitt Gray <william.gray@canonical.com>
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index a20368e1a720..ac4c84361be0 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -607,9 +607,18 @@ static void __clocksource_select(bool skipcur) */ if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { /* Override clocksource cannot be used. */ - pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n", - cs->name); - override_name[0] = 0; + if (cs->flags & CLOCK_SOURCE_UNSTABLE) { + pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", + cs->name); + override_name[0] = 0; + } else { + /* + * The override cannot be currently verified. + * Deferring to let the watchdog check. + */ + pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", + cs->name); + } } else /* Override clocksource can be used. */ best = cs;