[PATCH] oom: don't kill current when another OOM in progress
A previous patch to allow an exiting task to OOM kill itself (and thereby
avoid a little deadlock) introduced a problem. We don't want the
PF_EXITING task, even if it is 'current', to access mem reserves if there
is already a TIF_MEMDIE process in the system sucking up reserves.
Also make the commenting a little bit clearer, and note that our current
scheme of effectively single threading the OOM killer is not itself
perfect.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a5493a3..20f41b0 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -216,6 +216,18 @@
continue;
/*
+ * This task already has access to memory reserves and is
+ * being killed. Don't allow any other task access to the
+ * memory reserve.
+ *
+ * Note: this may have a chance of deadlock if it gets
+ * blocked waiting for another task which itself is waiting
+ * for memory. Is there a better alternative?
+ */
+ if (test_tsk_thread_flag(p, TIF_MEMDIE))
+ return ERR_PTR(-1UL);
+
+ /*
* This is in the process of releasing memory so wait for it
* to finish before killing some other task by mistake.
*
@@ -223,16 +235,15 @@
* go ahead if it is exiting: this will simply set TIF_MEMDIE,
* which will allow it to gain access to memory reserves in
* the process of exiting and releasing its resources.
- * Otherwise we could get an OOM deadlock.
+ * Otherwise we could get an easy OOM deadlock.
*/
- if ((p->flags & PF_EXITING) && p == current) {
+ if (p->flags & PF_EXITING) {
+ if (p != current)
+ return ERR_PTR(-1UL);
+
chosen = p;
*ppoints = ULONG_MAX;
- break;
}
- if ((p->flags & PF_EXITING) ||
- test_tsk_thread_flag(p, TIF_MEMDIE))
- return ERR_PTR(-1UL);
if (p->oomkilladj == OOM_DISABLE)
continue;