sparc64: Fix tsb_grow() in atomic context.

If our first THP installation for an MM is via the set_pmd_at() done
during khugepaged's collapsing we'll end up in tsb_grow() trying to do
a GFP_KERNEL allocation with several locks held.

Simply using GFP_ATOMIC in this situation is not the best option
because we really can't have this fail, so we'd really like to keep
this an order 0 GFP_KERNEL allocation if possible.

Also, doing the TSB allocation from khugepaged is a really bad idea
because we'll allocate it potentially from the wrong NUMA node in that
context.

So what we do is defer the hugepage TSB allocation until the first TLB
miss we take on a hugepage.  This is slightly tricky because we have
to handle two unusual cases:

1) Taking the first hugepage TLB miss in the window trap handler.
   We'll call the winfix_trampoline when that is detected.

2) An initial TSB allocation via TLB miss races with a hugetlb
   fault on another cpu running the same MM.  We handle this by
   unconditionally loading the TSB we see into the current cpu
   even if it's non-NULL at hugetlb_setup time.

Reported-by: Meelis Roos <mroos@ut.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/arch/sparc/mm/tlb.c b/arch/sparc/mm/tlb.c
index 3e8fec391fe0..ba6ae7ffdc2c 100644
--- a/arch/sparc/mm/tlb.c
+++ b/arch/sparc/mm/tlb.c
@@ -135,8 +135,15 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 			mm->context.huge_pte_count++;
 		else
 			mm->context.huge_pte_count--;
-		if (mm->context.huge_pte_count == 1)
-			hugetlb_setup(mm);
+
+		/* Do not try to allocate the TSB hash table if we
+		 * don't have one already.  We have various locks held
+		 * and thus we'll end up doing a GFP_KERNEL allocation
+		 * in an atomic context.
+		 *
+		 * Instead, we let the first TLB miss on a hugepage
+		 * take care of this.
+		 */
 	}
 
 	if (!pmd_none(orig)) {