[POWERPC] Fix deadlock with mmu_hash_lock in hash_page_sync

hash_page_sync() takes and releases the low level mmu hash
lock in order to sync with other processors disposing of page
tables.  Because that lock can be needed to service hash misses
triggered by interrupt handlers, taking it must be done with
interrupts off.  However, hash_page_sync() appears to be called
with interrupts enabled, thus causing occasional deadlocks.

We fix it by making sure hash_page_sync() masks interrupts while
holding the lock.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/arch/powerpc/mm/hash_low_32.S b/arch/powerpc/mm/hash_low_32.S
index 7f830a4888d6..e10d76a860d3 100644
--- a/arch/powerpc/mm/hash_low_32.S
+++ b/arch/powerpc/mm/hash_low_32.S
@@ -44,6 +44,9 @@ mmu_hash_lock:
 #ifdef CONFIG_SMP
         .text
 _GLOBAL(hash_page_sync)
+        mfmsr   r10
+        rlwinm  r0,r10,0,17,15          /* clear bit 16 (MSR_EE) */
+        mtmsr   r0
         lis     r8,mmu_hash_lock@h
         ori     r8,r8,mmu_hash_lock@l
         lis     r0,0x0fff
@@ -60,8 +63,9 @@ _GLOBAL(hash_page_sync)
         eieio
         li      r0,0
         stw     r0,0(r8)
-        blr     
-#endif
+        mtmsr   r10
+        blr
+#endif /* CONFIG_SMP */
 
 /*
  * Load a PTE into the hash table, if possible.