[PATCH 08 of 24] don't depend on PF_EXITING tasks to go away

[Andrea Arcangeli <andrea@suse.de>]

# HG changeset patch
# User Andrea Arcangeli <andrea@suse.de>
# Date 1187778125 -7200
# Node ID ffdc30241856d7155ceedd4132eef684f7cc7059
# Parent  b66d8470c04ed836787f69c7578d5fea4f18c322
don't depend on PF_EXITING tasks to go away

A PF_EXITING task don't have TIF_MEMDIE set so it might get stuck in
memory allocations without access to the PF_MEMALLOC pool (said that
ideally do_exit would better not require memory allocations, especially
not before calling exit_mm). The same way we raise its privilege to
TIF_MEMDIE if it's the current task, we should do it even if it's not
the current task to speedup oom killing.

Signed-off-by: Andrea Arcangeli <andrea@suse.de>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -234,27 +234,13 @@ static struct task_struct *select_bad_pr
 		 * 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?
+		 *
+		 * Better not to skip PF_EXITING tasks, since they
+		 * don't have access to the PF_MEMALLOC pool until
+		 * we select them here first.
 		 */
 		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.
-		 *
-		 * However, if p is the current task, we allow the 'kill' to
-		 * 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 easy OOM deadlock.
-		 */
-		if (p->flags & PF_EXITING) {
-			if (p != current)
-				return ERR_PTR(-1UL);
-
-			chosen = p;
-			*ppoints = ULONG_MAX;
-		}
 
 		if (p->oomkilladj == OOM_DISABLE)
 			continue;

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