[PATCH] [mmotm v2] comment on swap notify locking constraints

[PATCH] [mmotm v2] comment on swap notify locking constraints

[Nitin Gupta]

A block device makes swap_slot_free_notify() callback
when the last reference to a swap slot is dropped.

This callback is made under swap_lock and page table
lock. This is a note of warning for registered callback
function which must meet these constraints.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---
 include/linux/blkdev.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f86df8b..fb7b3c2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1294,6 +1294,7 @@ struct block_device_operations {
 						unsigned long long);
 	int (*revalidate_disk) (struct gendisk *);
 	int (*getgeo)(struct block_device *, struct hd_geometry *);
+	/* this callback is with swap_lock and page table lock held */
 	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
 	struct module *owner;
 };
-- 
1.6.2.5

Re: [PATCH] [mmotm v2] comment on swap notify locking constraints

[Hugh Dickins]

From: Nitin Gupta <ngupta@vflare.org>

A block device makes swap_slot_free_notify() callback
when the last reference to a swap slot is dropped.

This callback is made under swap_lock and sometimes page table
lock. This is a note of warning for registered callback
function which must meet these constraints.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---
I've added "sometimes " in the comment above and the comment below:
sorry, I should have made that clearer when I made this point.

Hugh

 include/linux/blkdev.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f86df8b..fb7b3c2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1294,6 +1294,7 @@ struct block_device_operations {
 						unsigned long long);
 	int (*revalidate_disk) (struct gendisk *);
 	int (*getgeo)(struct block_device *, struct hd_geometry *);
+	/* this callback is with swap_lock and sometimes page table lock held */
 	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
 	struct module *owner;
 };
-- 
1.6.2.5