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>

diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index 5f1fdeb92b8bce2c6ddd5a1e00aee4d3f8a40162..bcba1592ee21bf7820417f659d23e75db80e70b3 100644 (file)
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -204,9 +204,14 @@ 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;
@@ -228,6 +233,8 @@ 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;
        }
@@ -301,7 +308,7 @@ 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;
 
@@ -666,7 +673,7 @@ 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. */