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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>
This commit is contained in:
Omar Sandoval 2018-08-21 21:54:55 -07:00 committed by Linus Torvalds
parent a8dd9c4df1
commit bf53183164
1 changed files with 2 additions and 4 deletions
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6
fs/proc/kcore.c
View File

@ -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;
}