arch/tile: don't wait for migrating PTEs in an NMI handler

Doing so raises the possibility of self-deadlock if we are waiting
for a backtrace for an oprofile or perf interrupt while we are
in the middle of migrating our own stack page.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index cac17c4f2ecf..a1da473c8555 100644
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -203,9 +203,14 @@ static pgd_t *get_current_pgd(void)
  * interrupt or a critical region, and must do as little as possible.
  * Similarly, we can't use atomic ops here, since we may be handling a
  * fault caused by an atomic op access.
+ *
+ * If we find a migrating PTE while we're in an NMI context, and we're
+ * at a PC that has a registered exception handler, we don't wait,
+ * since this thread may (e.g.) have been interrupted while migrating
+ * its own stack, which would then cause us to self-deadlock.
  */
 static int handle_migrating_pte(pgd_t *pgd, int fault_num,
-                                unsigned long address,
+                                unsigned long address, unsigned long pc,
                                 int is_kernel_mode, int write)
 {
         pud_t *pud;
@@ -227,6 +232,8 @@ static int handle_migrating_pte(pgd_t *pgd, int fault_num,
                 pte_offset_kernel(pmd, address);
         pteval = *pte;
         if (pte_migrating(pteval)) {
+                if (in_nmi() && search_exception_tables(pc))
+                        return 0;
                 wait_for_migration(pte);
                 return 1;
         }
@@ -300,7 +307,7 @@ static int handle_page_fault(struct pt_regs *regs,
          * rather than trying to patch up the existing PTE.
          */
         pgd = get_current_pgd();
-        if (handle_migrating_pte(pgd, fault_num, address,
+        if (handle_migrating_pte(pgd, fault_num, address, regs->pc,
                                  is_kernel_mode, write))
                 return 1;
 
@@ -665,7 +672,7 @@ struct intvec_state do_page_fault_ics(struct pt_regs *regs, int fault_num,
          */
         if (fault_num == INT_DTLB_ACCESS)
                 write = 1;
-        if (handle_migrating_pte(pgd, fault_num, address, 1, write))
+        if (handle_migrating_pte(pgd, fault_num, address, pc, 1, write))
                 return state;
 
         /* Return zero so that we continue on with normal fault handling. */