mm: Remove i_mmap_lock lockbreak

Hugh says:
 "The only significant loser, I think, would be page reclaim (when
  concurrent with truncation): could spin for a long time waiting for
  the i_mmap_mutex it expects would soon be dropped? "

Counter points:
 - cpu contention makes the spin stop (need_resched())
 - zap pages should be freeing pages at a higher rate than reclaim
   ever can

I think the simplification of the truncate code is definitely worth it.

Effectively reverts: 2aa15890f3c ("mm: prevent concurrent
unmap_mapping_range() on the same inode") and takes out the code that
caused its problem.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 12 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 40d49986e714..50cb04bb56bf 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -445,10 +445,8 @@ static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
         if (vma->vm_file)
                 mapping = vma->vm_file->f_mapping;
 
-        if (mapping) {
+        if (mapping)
                 spin_lock(&mapping->i_mmap_lock);
-                vma->vm_truncate_count = mapping->truncate_count;
-        }
 
         __vma_link(mm, vma, prev, rb_link, rb_parent);
         __vma_link_file(vma);
@@ -558,16 +556,7 @@ again:			remove_next = 1 + (end > next->vm_end);
                 if (!(vma->vm_flags & VM_NONLINEAR))
                         root = &mapping->i_mmap;
                 spin_lock(&mapping->i_mmap_lock);
-                if (importer &&
-                    vma->vm_truncate_count != next->vm_truncate_count) {
-                        /*
-                         * unmap_mapping_range might be in progress:
-                         * ensure that the expanding vma is rescanned.
-                         */
-                        importer->vm_truncate_count = 0;
-                }
                 if (insert) {
-                        insert->vm_truncate_count = vma->vm_truncate_count;
                         /*
                          * Put into prio_tree now, so instantiated pages
                          * are visible to arm/parisc __flush_dcache_page