Commit e2a8f20d authored by Baoquan He's avatar Baoquan He Committed by Andrew Morton
Browse files

Crash: add lock to serialize crash hotplug handling 

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@redhat.com


Fixes: 24726275 ("crash: add generic infrastructure for crash hotplug support")
Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Tested-by: default avatarEric DeVolder <eric.devolder@oracle.com>
Reviewed-by: default avatarEric DeVolder <eric.devolder@oracle.com>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent bbe246f8

kernel/crash_core.c

+17 −0
Original line number Diff line number Diff line
@@ -739,6 +739,17 @@ subsys_initcall(crash_notes_memory_init); 
#undef pr_fmt

#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
@@ -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(unsigned int hp_action, unsigned int cpu) 
{

	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(unsigned int hp_action, unsigned int cpu) 
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)