The patch titled
Subject: fs/proc: fix softlockup in __read_vmcore (part 2)
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
fs-proc-fix-softlockup-in-__read_vmcore-part-2.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-fix-softlockup-in-__read_vmcore-part-2.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Rik van Riel <riel@xxxxxxxxxxx>
Subject: fs/proc: fix softlockup in __read_vmcore (part 2)
Date: Fri, 10 Jan 2025 10:28:21 -0500
Since commit 5cbcb62dddf5 ("fs/proc: fix softlockup in __read_vmcore") the
number of softlockups in __read_vmcore at kdump time have gone down, but
they still happen sometimes.
In a memory constrained environment like the kdump image, a softlockup is
not just a harmless message, but it can interfere with things like RCU
freeing memory, causing the crashdump to get stuck.
The second loop in __read_vmcore has a lot more opportunities for natural
sleep points, like scheduling out while waiting for a data write to
happen, but apparently that is not always enough.
Add a cond_resched() to the second loop in __read_vmcore to (hopefully)
get rid of the softlockups.
Link: https://lkml.kernel.org/r/20250110102821.2a37581b@fangorn
Fixes: 5cbcb62dddf5 ("fs/proc: fix softlockup in __read_vmcore")
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Reported-by: Breno Leitao <leitao@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/vmcore.c | 2 ++
1 file changed, 2 insertions(+)
--- a/fs/proc/vmcore.c~fs-proc-fix-softlockup-in-__read_vmcore-part-2
+++ a/fs/proc/vmcore.c
@@ -404,6 +404,8 @@ static ssize_t __read_vmcore(struct iov_
if (!iov_iter_count(iter))
return acc;
}
+
+ cond_resched();
}
return acc;
_
Patches currently in -mm which might be from riel@xxxxxxxxxxx are
fs-proc-fix-softlockup-in-__read_vmcore-part-2.patch
mm-remove-unnecessary-calls-to-lru_add_drain.patch
