The patch titled
Subject: Crash: add lock to serialize crash hotplug handling
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
crash-add-lock-to-serialize-crash-hotplug-handling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/crash-add-lock-to-serialize-crash-hotplug-handling.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: Baoquan He <bhe@xxxxxxxxxx>
Subject: Crash: add lock to serialize crash hotplug handling
Date: Tue, 26 Sep 2023 20:09:05 +0800
Eric reported that handling corresponding crash hotplug event can be
failed easily when many memory hotplug event are notified in a short
period. They failed because failing to take __kexec_lock.
=======
[ 78.714569] Fallback order for Node 0: 0
[ 78.714575] Built 1 zonelists, mobility grouping on. Total pages: 1817886
[ 78.717133] Policy zone: Normal
[ 78.724423] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[ 78.727207] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[ 80.056643] PEFILE: Unsigned PE binary
=======
The memory hotplug events are notified very quickly and very many, while
the handling of crash hotplug is much slower relatively. So the atomic
variable __kexec_lock and kexec_trylock() can't guarantee the
serialization of crash hotplug handling.
Here, add a new mutex lock __crash_hotplug_lock to serialize crash hotplug
handling specifically. This doesn't impact the usage of __kexec_lock.
Link: https://lkml.kernel.org/r/20230926120905.392903-1-bhe@xxxxxxxxxx
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Tested-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
Reviewed-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
Cc: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/crash_core.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
--- a/kernel/crash_core.c~crash-add-lock-to-serialize-crash-hotplug-handling
+++ a/kernel/crash_core.c
@@ -740,6 +740,17 @@ subsys_initcall(crash_notes_memory_init)
#define pr_fmt(fmt) "crash hp: " fmt
/*
+ * Different than kexec/kdump loading/unloading/jumping/shrinking which
+ * usually rarely happen, there will be many crash hotplug events notified
+ * during one short period, e.g one memory board is hot added and memory
+ * regions are online. So mutex lock __crash_hotplug_lock is used to
+ * serialize the crash hotplug handling specifically.
+ */
+DEFINE_MUTEX(__crash_hotplug_lock);
+#define crash_hotplug_lock() mutex_lock(&__crash_hotplug_lock)
+#define crash_hotplug_unlock() mutex_unlock(&__crash_hotplug_lock)
+
+/*
* This routine utilized when the crash_hotplug sysfs node is read.
* It reflects the kernel's ability/permission to update the crash
* elfcorehdr directly.
@@ -748,9 +759,11 @@ int crash_check_update_elfcorehdr(void)
{
int rc = 0;
+ crash_hotplug_lock();
/* Obtain lock while reading crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
+ crash_hotplug_unlock();
return 0;
}
if (kexec_crash_image) {
@@ -761,6 +774,7 @@ int crash_check_update_elfcorehdr(void)
}
/* Release lock now that update complete */
kexec_unlock();
+ crash_hotplug_unlock();
return rc;
}
@@ -783,9 +797,11 @@ static void crash_handle_hotplug_event(u
{
struct kimage *image;
+ crash_hotplug_lock();
/* Obtain lock while changing crash information */
if (!kexec_trylock()) {
pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
+ crash_hotplug_unlock();
return;
}
@@ -852,6 +868,7 @@ static void crash_handle_hotplug_event(u
out:
/* Release lock now that update complete */
kexec_unlock();
+ crash_hotplug_unlock();
}
static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
_
Patches currently in -mm which might be from bhe@xxxxxxxxxx are
crash-add-lock-to-serialize-crash-hotplug-handling.patch
crash_corec-remove-unnecessary-parameter-of-function.patch
crash_core-change-the-prototype-of-function-parse_crashkernel.patch
crash_core-change-parse_crashkernel-to-support-crashkernel=highlow-parsing.patch
crash_core-add-generic-function-to-do-reservation.patch
crash_core-move-crashk_res-definition-into-crash_corec.patch
x86-kdump-use-generic-interface-to-simplify-crashkernel-reservation-code.patch
x86-kdump-use-generic-interface-to-simplify-crashkernel-reservation-code-fix.patch
arm64-kdump-use-generic-interface-to-simplify-crashkernel-reservation.patch
riscv-kdump-use-generic-interface-to-simplify-crashkernel-reservation.patch
crash_corec-remove-unneeded-functions.patch
