linux-kernel - [PATCH v3 1/8] proc/kcore: don't grab lock for kclist

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Message-Id: <98208db1faf167aa8b08eebfa968d95c70527739.1531953780.git.osandov@fb.com>
Date:   Wed, 18 Jul 2018 15:58:41 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        James Morse <james.morse@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>, kernel-team@...com
Subject: [PATCH v3 1/8] proc/kcore: don't grab lock for kclist_add()

From: Omar Sandoval <osandov@...com>

kclist_add() is only called at init time, so there's no point in
grabbing any locks. We're also going to replace the rwlock with a rwsem,
which we don't want to try grabbing during early boot.

While we're here, mark kclist_add() with __init so that we'll get a
warning if it's called from non-init code.

Signed-off-by: Omar Sandoval <osandov@...com>
---
 fs/proc/kcore.c       | 7 +++----
 include/linux/kcore.h | 2 +-
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 66c373230e60..b0b9a76f28d6 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -62,16 +62,15 @@ static LIST_HEAD(kclist_head);
 static DEFINE_RWLOCK(kclist_lock);
 static int kcore_need_update = 1;
 
-void
-kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
+/* This doesn't grab kclist_lock, so it should only be used at init time. */
+void __init kclist_add(struct kcore_list *new, void *addr, size_t size,
+		       int type)
 {
 	new->addr = (unsigned long)addr;
 	new->size = size;
 	new->type = type;
 
-	write_lock(&kclist_lock);
 	list_add_tail(&new->list, &kclist_head);
-	write_unlock(&kclist_lock);
 }
 
 static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
diff --git a/include/linux/kcore.h b/include/linux/kcore.h
index 8de55e4b5ee9..c20f296438fb 100644
--- a/include/linux/kcore.h
+++ b/include/linux/kcore.h
@@ -35,7 +35,7 @@ struct vmcoredd_node {
 };
 
 #ifdef CONFIG_PROC_KCORE
-extern void kclist_add(struct kcore_list *, void *, size_t, int type);
+void __init kclist_add(struct kcore_list *, void *, size_t, int type);
 #else
 static inline
 void kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
-- 
2.18.0