[PATCH] lazy tlb: consolidate lazy tlb mm switching fix
Nicholas Piggin
npiggin at gmail.com
Wed Jun 7 10:56:22 AEST 2023
Fix an upstream powerpc bug that was discovered with a WARN_ON added in
"lazy tlb: consolidate lazy tlb mm switching":
Switching mm and tinkering with current->active_mm should be done with
irqs disabled. There is a path where exit_lazy_flush_tlb can be called
with irqs enabled:
exit_lazy_flush_tlb
flush_type_needed
__flush_all_mm
tlb_finish_mmu
exit_mmap
Which results in the switching being incorrectly with irqs enabled.
Link: https://lore.kernel.org/linuxppc-dev/87a5xcgopc.fsf@mail.lhotse/T/#m105488939d0cd9f980978ed2fdeeb89bf731e673
Fixes: a665eec0a22e1 ("powerpc/64s/radix: Fix mm_cpumask trimming race vs k>
I will send that fix upstream, which will end up conflicting with these.
The resolution will be to take akpm's side of the merge (with this patch).
Or drop the patch when it conflicts and I'll resend it rebased on the fix.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/mm/book3s64/radix_tlb.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index 90953cf9f648..8d71fe8f5cdb 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -795,8 +795,16 @@ void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush)
goto out;
if (current->active_mm == mm) {
- /* Is a kernel thread and is using mm as the lazy tlb */
+ unsigned long flags;
+
+ /*
+ * It is a kernel thread and is using mm as the lazy tlb, so
+ * switch it to init_mm. This is not always called from IPI
+ * (e.g., flush_type_needed), so must disable irqs.
+ */
+ local_irq_save(flags);
kthread_end_lazy_tlb_mm();
+ local_irq_restore(flags);
}
/*
--
2.40.1
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