[PATCH] oom: handle current exiting

If current *is* exiting, it should actually be allowed to access reserved
memory rather than OOM kill something else.  Can't do this via a straight
check in page_alloc.c because that would allow multiple tasks to use up
reserves.  Instead cause current to OOM-kill itself which will mark it as
TIF_MEMDIE.

The current procedure of simply aborting the OOM-kill if a task is exiting can
lead to OOM deadlocks.

In the case of killing a PF_EXITING task, don't make a lot of noise about it.
This becomes more important in future patches, where we can "kill" OOM_DISABLE
tasks.

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 4f815b0..0131bae 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -210,11 +210,26 @@ static struct task_struct *select_bad_process(unsigned long *ppoints)
                /*
                 * 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 OOM deadlock.
                 */
                releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
                                                p->flags & PF_EXITING;
-               if (releasing && !(p->flags & PF_DEAD))
+               if (releasing) {
+                       /* PF_DEAD tasks have already released their mm */
+                       if (p->flags & PF_DEAD)
+                               continue;
+                       if (p->flags & PF_EXITING && p == current) {
+                               chosen = p;
+                               *ppoints = ULONG_MAX;
+                               break;
+                       }
                        return ERR_PTR(-1UL);
+               }
                if (p->flags & PF_SWAPOFF)
                        return p;
 
@@ -248,8 +263,11 @@ static void __oom_kill_task(struct task_struct *p, const char *message)
                return;
        }
        task_unlock(p);
-       printk(KERN_ERR "%s: Killed process %d (%s).\n",
+
+       if (message) {
+               printk(KERN_ERR "%s: Killed process %d (%s).\n",
                                message, p->pid, p->comm);
+       }
 
        /*
         * We give our sacrificial lamb high priority and access to
@@ -300,8 +318,17 @@ static int oom_kill_process(struct task_struct *p, unsigned long points,
        struct task_struct *c;
        struct list_head *tsk;
 
-       printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li and "
-               "children.\n", p->pid, p->comm, points);
+       /*
+        * If the task is already exiting, don't alarm the sysadmin or kill
+        * its children or threads, just set TIF_MEMDIE so it can die quickly
+        */
+       if (p->flags & PF_EXITING) {
+               __oom_kill_task(p, NULL);
+               return 0;
+       }
+
+       printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li"
+                       " and children.\n", p->pid, p->comm, points);
        /* Try to kill a child first */
        list_for_each(tsk, &p->children) {
                c = list_entry(tsk, struct task_struct, sibling);