The patch titled
Subject: proc/kcore: don't grab lock for memory hotplug notifier
has been added to the -mm tree. Its filename is
proc-kcore-dont-grab-lock-for-memory-hotplug-notifier.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/proc-kcore-dont-grab-lock-for-memory-hotplug-notifier.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/proc-kcore-dont-grab-lock-for-memory-hotplug-notifier.patch
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------------------------------------------------------
From: Omar Sandoval <osandov@xxxxxx>
Subject: 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@xxxxxx
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/kcore.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff -puN fs/proc/kcore.c~proc-kcore-dont-grab-lock-for-memory-hotplug-notifier fs/proc/kcore.c
--- a/fs/proc/kcore.c~proc-kcore-dont-grab-lock-for-memory-hotplug-notifier
+++ a/fs/proc/kcore.c
@@ -118,7 +118,7 @@ static void __kcore_update_ram(struct li
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 li
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(stru
switch (action) {
case MEM_ONLINE:
case MEM_OFFLINE:
- write_lock(&kclist_lock);
kcore_need_update = 1;
- write_unlock(&kclist_lock);
+ break;
}
return NOTIFY_OK;
}
_
Patches currently in -mm which might be from osandov@xxxxxx are
proc-kcore-dont-grab-lock-for-kclist_add.patch
proc-kcore-dont-grab-lock-for-memory-hotplug-notifier.patch
proc-kcore-replace-kclist_lock-rwlock-with-rwsem.patch
proc-kcore-fix-memory-hotplug-vs-multiple-opens-race.patch
proc-kcore-hold-lock-during-read.patch
proc-kcore-clean-up-elf-header-generation.patch
proc-kcore-optimize-multiple-page-reads.patch
proc-kcore-add-vmcoreinfo-note-to-proc-kcore.patch
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