fs/proc: fix softlockup in __read_vmcore (part 2)

commit cbc5dde0a461240046e8a41c43d7c3b76d5db952 upstream.

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@surriel.com>
Reported-by: Breno Leitao <leitao@debian.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 17b320bbf5c4f46987a92bee24bbaeddf4cd56a6..7a757d387ca0df277ffbe06ee72ad40c3baa01d8 100644 (file)
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -396,6 +396,8 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
                        if (buflen == 0)
                                return acc;
                }
+
+               cond_resched();
        }
 
        return acc;