linux-kernel - [PATCH] mm, oom: OOM sysrq should always kill a process

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Date:   Wed,  5 Jan 2022 18:51:15 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Jann Horn <jannh@...gle.com>
Subject: [PATCH] mm, oom: OOM sysrq should always kill a process

The OOM kill sysrq (alt+sysrq+F) should allow the user to kill the
process with the highest OOM badness with a single execution.

However, at the moment, the OOM kill can bail out if an OOM notifier
(e.g. the i915 one) says that it reclaimed a tiny amount of memory
from somewhere. That's probably not what the user wants.

As documented in struct oom_control, order == -1 means the oom kill is
required by sysrq. So check for that, and if it's true, don't bail out
no matter what the OOM notifiers say.

Signed-off-by: Jann Horn <jannh@...gle.com>
---
 mm/oom_kill.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1ddabefcfb5a..dc645cbc6e0d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1051,13 +1051,14 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifier);
 bool out_of_memory(struct oom_control *oc)
 {
 	unsigned long freed = 0;
+	bool sysrq_forced = oc->order == -1;

 	if (oom_killer_disabled)
 		return false;

 	if (!is_memcg_oom(oc)) {
 		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
-		if (freed > 0)
+		if (freed > 0 && !sysrq_forced)
 			/* Got some memory back in the last second. */
 			return true;
 	}

base-commit: c9e6606c7fe92b50a02ce51dda82586ebdf99b48
-- 
2.34.1.448.ga2b2bfdf31-goog