Commit bf531831 authored Aug 21, 2018 by Omar Sandoval Committed by Linus Torvalds Aug 22, 2018

proc/kcore: don't grab lock for memory hotplug notifier

The memory hotplug notifier kcore_callback() only needs kclist_lock to
prevent races with __kcore_update_ram(), but we can easily eliminate that
race by using an atomic xchg() in __kcore_update_ram().  This is
preparation for converting kclist_lock to an rwsem.

Link: http://lkml.kernel.org/r/0a4bc89f4dbde8b5b2ea309f7b4fb6a85fe29df2.1531953780.git.osandov@fb.com


Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent a8dd9c4d

fs/proc/kcore.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -118,7 +118,7 @@ static void __kcore_update_ram(struct list_head *list)
		LIST_HEAD(garbage);

		write_lock(&kclist_lock);
		if (kcore_need_update) {
		if (xchg(&kcore_need_update, 0)) {
		list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
		if (pos->type == KCORE_RAM
		\|\| pos->type == KCORE_VMEMMAP)
		@@ -127,7 +127,6 @@ static void __kcore_update_ram(struct list_head *list)
		list_splice_tail(list, &kclist_head);
		} else
		list_splice(list, &garbage);
		kcore_need_update = 0;
		proc_root_kcore->size = get_kcore_size(&nphdr, &size);
		write_unlock(&kclist_lock);

		@@ -593,9 +592,8 @@ static int __meminit kcore_callback(struct notifier_block *self,
		switch (action) {
		case MEM_ONLINE:
		case MEM_OFFLINE:
		write_lock(&kclist_lock);
		kcore_need_update = 1;
		write_unlock(&kclist_lock);
		break;
		}
		return NOTIFY_OK;
		}