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

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Message-ID: <alpine.LSU.2.00.1001141845110.15495@sister.anvils>
Date:	Thu, 14 Jan 2010 18:50:22 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Nitin Gupta <ngupta@...are.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [mmotm v2] comment on swap notify locking constraints

From: Nitin Gupta <ngupta@...are.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@...are.org>
Signed-off-by: Hugh Dickins <hugh.dickins@...cali.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
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