linux-kernel - [PATCH] fs/proc: fix softlockup in __read

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Date: Tue, 7 May 2024 09:18:58 -0400
From: Rik van Riel <riel@...riel.com>
To: Baoquan He <bhe@...hat.com>
Cc: Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
 kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, kernel-team@...a.com
Subject: [PATCH] fs/proc: fix softlockup in __read_vmcore

While taking a kernel core dump with makedumpfile on a larger system,
softlockup messages often appear.

While softlockup warnings can be harmless, they can also interfere
with things like RCU freeing memory, which can be problematic when
the kdump kexec image is configured with as little memory as possible.

Avoid the softlockup, and give things like work items and RCU a
chance to do their thing during __read_vmcore by adding a cond_resched.

Signed-off-by: Rik van Riel <riel@...riel.com>
---
 fs/proc/vmcore.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 1fb213f379a5..d06607a1f137 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -383,6 +383,8 @@ static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
 		/* leave now if filled buffer already */
 		if (!iov_iter_count(iter))
 			return acc;
+
+		cond_resched();
 	}

 	list_for_each_entry(m, &vmcore_list, list) {
-- 
2.42.0