[34-longterm 095/209] perf_events: Fix perf_counter_mmap() hook in mprotect()

[Paul Gortmaker]

From: Pekka Enberg <penberg@xxxxxxxxxx>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 63bfd7384b119409685a17d5c58f0b56e5dc03da upstream.

As pointed out by Linus, commit dab5855 ("perf_counter: Add mmap event hooks to
mprotect()") is fundamentally wrong as mprotect_fixup() can free 'vma' due to
merging. Fix the problem by moving perf_event_mmap() hook to
mprotect_fixup().

Note: there's another successful return path from mprotect_fixup() if old
flags equal to new flags. We don't, however, need to call
perf_event_mmap() there because 'perf' already knows the VMA is
executable.

Reported-by: Dave Jones <davej@xxxxxxxxxx>
Analyzed-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 mm/mprotect.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2d1bf7c..4c51338 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -211,6 +211,7 @@ success:
 	mmu_notifier_invalidate_range_end(mm, start, end);
 	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
+	perf_event_mmap(vma);
 	return 0;
 
 fail:
@@ -299,7 +300,6 @@ SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 		error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 		if (error)
 			goto out;
-		perf_event_mmap(vma);
 		nstart = tmp;
 
 		if (nstart < prev->vm_end)
-- 
1.7.4.4

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