There seems to be a mismatch in expectations between the powerpc arch code and the generic (and x86) code in terms of the irq state when switch_mm() is called.
powerpc expects irqs to already be (soft) disabled when switch_mm() is called, as made clear in the commit message of 9c1e105 "powerpc: Allow perf_counters to access user memory at interrupt time". That seems to be true when it's called from the schedule, but not for use_mm(). This becomes clear when looking at the x86 code paths for switch_mm(). There, switch_mm() itself disable irqs, with a switch_mm_irqs_off() variant which expects that to be already done. This patch addresses the problem, making the powerpc code mirror the x86 code. Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> --- arch/powerpc/include/asm/mmu_context.h | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) RH-Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1437794 It seems that some more recent changes in vhost have made it more likely to hit this problem, triggering a WARN. diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h index b9e3f0a..0012f03 100644 --- a/arch/powerpc/include/asm/mmu_context.h +++ b/arch/powerpc/include/asm/mmu_context.h @@ -70,8 +70,9 @@ extern void drop_cop(unsigned long acop, struct mm_struct *mm); * switch_mm is the entry point called from the architecture independent * code in kernel/sched/core.c */ -static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, - struct task_struct *tsk) +static inline void switch_mm_irqs_off(struct mm_struct *prev, + struct mm_struct *next, + struct task_struct *tsk) { /* Mark this context has been used on the new CPU */ if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next))) @@ -110,6 +111,18 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, switch_mmu_context(prev, next, tsk); } +static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, + struct task_struct *tsk) +{ + unsigned long flags; + + local_irq_save(flags); + switch_mm_irqs_off(prev, next, tsk); + local_irq_restore(flags); +} +#define switch_mm_irqs_off switch_mm_irqs_off + + #define deactivate_mm(tsk,mm) do { } while (0) /* -- 2.9.3
