| Message ID | 20230607005601.583293-1-npiggin@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | dfaed3e1fa7099de8de4e89cbe7eb9c1bca27dfe |
| Headers | show |
| Series | powerpc/64s/radix: Fix exit lazy tlb mm switch with irqs enabled | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/github-powerpc_selftests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_ppctests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_sparse | success | Successfully ran 4 jobs. |
| snowpatch_ozlabs/github-powerpc_clang | success | Successfully ran 6 jobs. |
| snowpatch_ozlabs/github-powerpc_kernel_qemu | success | Successfully ran 24 jobs. |
> Reported-by: Sachin Sant <sachinp@linux.ibm.com> > Link: https://lore.kernel.org/linuxppc-dev/87a5xcgopc.fsf@mail.lhotse/T/#m105488939d0cd9f980978ed2fdeeb89bf731e673 > Fixes: a665eec0a22e1 ("powerpc/64s/radix: Fix mm_cpumask trimming race vs kthread_use_mm") > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> > --- > This sounds worse than it probably is, radix can likely tolerate an > interrupt hitting in mm switch, and the active_mm update may not be racy > in practice either. Still be good to backport it because I'm not 100% > sure of that. > > This path can be stressed by reducing tlb_mm_cpumask_trim_timer (e.g., > to 3). > > Thanks, > Nick > > arch/powerpc/mm/book3s64/radix_tlb.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > This patch fixes the reported warning. Ran powerpc selftests (with default value for tlb_mm_cpumask_trim_timer as well as tlb_mm_cpumask_trim_timer=3 ). No new errors were observed. Tested-by: Sachin Sant <sachinp@linux.ibm.com> - Sachin
On Wed, 07 Jun 2023 10:56:00 +1000, Nicholas Piggin wrote: > 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 > > [...] Applied to powerpc/fixes. [1/1] powerpc/64s/radix: Fix exit lazy tlb mm switch with irqs enabled https://git.kernel.org/powerpc/c/dfaed3e1fa7099de8de4e89cbe7eb9c1bca27dfe cheers
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c index ce804b7bf84e..0bd4866d9824 100644 --- a/arch/powerpc/mm/book3s64/radix_tlb.c +++ b/arch/powerpc/mm/book3s64/radix_tlb.c @@ -795,12 +795,20 @@ void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush) goto out; if (current->active_mm == mm) { + unsigned long flags; + WARN_ON_ONCE(current->mm != NULL); - /* Is a kernel thread and is using mm as the lazy tlb */ + /* + * 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); mmgrab_lazy_tlb(&init_mm); current->active_mm = &init_mm; switch_mm_irqs_off(mm, &init_mm, current); mmdrop_lazy_tlb(mm); + local_irq_restore(flags); } /*
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. Reported-by: Sachin Sant <sachinp@linux.ibm.com> Link: https://lore.kernel.org/linuxppc-dev/87a5xcgopc.fsf@mail.lhotse/T/#m105488939d0cd9f980978ed2fdeeb89bf731e673 Fixes: a665eec0a22e1 ("powerpc/64s/radix: Fix mm_cpumask trimming race vs kthread_use_mm") Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- This sounds worse than it probably is, radix can likely tolerate an interrupt hitting in mm switch, and the active_mm update may not be racy in practice either. Still be good to backport it because I'm not 100% sure of that. This path can be stressed by reducing tlb_mm_cpumask_trim_timer (e.g., to 3). Thanks, Nick arch/powerpc/mm/book3s64/radix_tlb.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)