x86/mm: Fix pgd_lock deadlock

It's forbidden to take the page_table_lock with the irq disabled
or if there's contention the IPIs (for tlb flushes) sent with
the page_table_lock held will never run leading to a deadlock.

Nobody takes the pgd_lock from irq context so the _irqsave can be
removed.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
LKML-Reference: <201102162345.p1GNjMjm021738@imap1.linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 7 deletions

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 500242d3c96d..0113d19c8aa6 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -121,14 +121,12 @@ static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
 
 static void pgd_dtor(pgd_t *pgd)
 {
-        unsigned long flags; /* can be called from interrupt context */
-
         if (SHARED_KERNEL_PMD)
                 return;
 
-        spin_lock_irqsave(&pgd_lock, flags);
+        spin_lock(&pgd_lock);
         pgd_list_del(pgd);
-        spin_unlock_irqrestore(&pgd_lock, flags);
+        spin_unlock(&pgd_lock);
 }
 
 /*
@@ -260,7 +258,6 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 {
         pgd_t *pgd;
         pmd_t *pmds[PREALLOCATED_PMDS];
-        unsigned long flags;
 
         pgd = (pgd_t *)__get_free_page(PGALLOC_GFP);
 
@@ -280,12 +277,12 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
          * respect to anything walking the pgd_list, so that they
          * never see a partially populated pgd.
          */
-        spin_lock_irqsave(&pgd_lock, flags);
+        spin_lock(&pgd_lock);
 
         pgd_ctor(mm, pgd);
         pgd_prepopulate_pmd(mm, pgd, pmds);
 
-        spin_unlock_irqrestore(&pgd_lock, flags);
+        spin_unlock(&pgd_lock);
 
         return pgd;