[PATCH] mm: powerpc ptlock comments

Update comments (only) on page_table_lock and mmap_sem in arch/powerpc.
Removed the comment on page_table_lock from hash_huge_page: since it's no
longer taking page_table_lock itself, it's irrelevant whether others are; but
how it is safe (even against huge file truncation?) I can't say.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/powerpc/mm/tlb_32.c b/arch/powerpc/mm/tlb_32.c
index 6c3dc3c44c86..ad580f3742e5 100644
--- a/arch/powerpc/mm/tlb_32.c
+++ b/arch/powerpc/mm/tlb_32.c
@@ -149,6 +149,12 @@ void flush_tlb_mm(struct mm_struct *mm)
                 return;
         }
 
+        /*
+         * It is safe to go down the mm's list of vmas when called
+         * from dup_mmap, holding mmap_sem.  It would also be safe from
+         * unmap_region or exit_mmap, but not from vmtruncate on SMP -
+         * but it seems dup_mmap is the only SMP case which gets here.
+         */
         for (mp = mm->mmap; mp != NULL; mp = mp->vm_next)
                 flush_range(mp->vm_mm, mp->vm_start, mp->vm_end);
         FINISH_FLUSH;