path: root/arch/sparc/kernel/smp_64.c
diff options
authorDavid S. Miller <>2009-03-27 01:09:17 -0700
committerDavid S. Miller <>2009-03-27 01:09:17 -0700
commitf9384d41c02408dd404aa64d66d0ef38adcf6479 (patch)
tree3eba745ae1cd20ae2b14dcdbe21efd05cd33fd27 /arch/sparc/kernel/smp_64.c
parent86ee79c3dbd48d7430fd81edc1da3516c9f6dabc (diff)
sparc64: Fix MM refcount check in smp_flush_tlb_pending().
As explained by Benjamin Herrenschmidt: > CPU 0 is running the context, task->mm == task->active_mm == your > context. The CPU is in userspace happily churning things. > > CPU 1 used to run it, not anymore, it's now running fancyfsd which > is a kernel thread, but current->active_mm still points to that > same context. > > Because there's only one "real" user, mm_users is 1 (but mm_count is > elevated, it's just that the presence on CPU 1 as active_mm has no > effect on mm_count(). > > At this point, fancyfsd decides to invalidate a mapping currently mapped > by that context, for example because a networked file has changed > remotely or something like that, using unmap_mapping_ranges(). > > So CPU 1 goes into the zapping code, which eventually ends up calling > flush_tlb_pending(). Your test will succeed, as current->active_mm is > indeed the target mm for the flush, and mm_users is indeed 1. So you > will -not- send an IPI to the other CPU, and CPU 0 will continue happily > accessing the pages that should have been unmapped. To fix this problem, check ->mm instead of ->active_mm, and this means: > So if you test current->mm, you effectively account for mm_users == 1, > so the only way the mm can be active on another processor is as a lazy > mm for a kernel thread. So your test should work properly as long > as you don't have a HW that will do speculative TLB reloads into the > TLB on that other CPU (and even if you do, you flush-on-switch-in should > get rid of any crap here). And therefore we should be OK. Signed-off-by: David S. Miller <>
Diffstat (limited to 'arch/sparc/kernel/smp_64.c')
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
index 6cd1a5b65067..79457f682b5a 100644
--- a/arch/sparc/kernel/smp_64.c
+++ b/arch/sparc/kernel/smp_64.c
@@ -1031,7 +1031,7 @@ void smp_fetch_global_regs(void)
* If the address space is non-shared (ie. mm->count == 1) we avoid
* cross calls when we want to flush the currently running process's
* tlb state. This is done by clearing all cpu bits except the current
- * processor's in current->active_mm->cpu_vm_mask and performing the
+ * processor's in current->mm->cpu_vm_mask and performing the
* flush locally only. This will force any subsequent cpus which run
* this task to flush the context from the local tlb if the process
* migrates to another cpu (again).
@@ -1074,7 +1074,7 @@ void smp_flush_tlb_pending(struct mm_struct *mm, unsigned long nr, unsigned long
u32 ctx = CTX_HWBITS(mm->context);
int cpu = get_cpu();
- if (mm == current->active_mm && atomic_read(&mm->mm_users) == 1)
+ if (mm == current->mm && atomic_read(&mm->mm_users) == 1)
mm->cpu_vm_mask = cpumask_of_cpu(cpu);