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authorLee Schermerhorn <lee.schermerhorn@hp.com>2008-04-28 02:13:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-28 08:58:23 -0700
commitf4e53d910b7dde2685b177f1e7c3e3e0b4a42f7b (patch)
treedb4db3abbc0b63de88dabd13e9359ca86973935c
parent846a16bf0fc80dc95a414ffce465e3cbf9680247 (diff)
mempolicy: write lock mmap_sem while changing task mempolicy
A read of /proc/<pid>/numa_maps holds the target task's mmap_sem for read while examining each vma's mempolicy. A vma's mempolicy can fall back to the task's policy. However, the task could be changing it's task policy and free the one that the show_numa_maps() is examining. To prevent this, grab the mmap_sem for write when updating task mempolicy. Pointed out to me by Christoph Lameter and extracted and reworked from Christoph's alternative mempol reference counting patch. This is analogous to the way that do_mbind() and do_get_mempolicy() prevent races between task's sharing an mm_struct [a.k.a. threads] setting and querying a mempolicy for a particular address. Note: this is necessary, but not sufficient, to allow us to stop taking an extra reference on "other task's mempolicy" in get_vma_policy. Subsequent patches will complete this update, allowing us to simplify the tests for whether we need to unref a mempolicy at various points in the code. Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Christoph Lameter <clameter@sgi.com> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/mempolicy.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e9fc1c1ae66..c6c61ea6bb8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -591,16 +591,29 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
nodemask_t *nodes)
{
struct mempolicy *new;
+ struct mm_struct *mm = current->mm;
new = mpol_new(mode, flags, nodes);
if (IS_ERR(new))
return PTR_ERR(new);
+
+ /*
+ * prevent changing our mempolicy while show_numa_maps()
+ * is using it.
+ * Note: do_set_mempolicy() can be called at init time
+ * with no 'mm'.
+ */
+ if (mm)
+ down_write(&mm->mmap_sem);
mpol_put(current->mempolicy);
current->mempolicy = new;
mpol_set_task_struct_flag();
if (new && new->policy == MPOL_INTERLEAVE &&
nodes_weight(new->v.nodes))
current->il_next = first_node(new->v.nodes);
+ if (mm)
+ up_write(&mm->mmap_sem);
+
return 0;
}