From: Miao Xie Subject: [PATCH 1/4] vfs: introduce try_to_writeback_inodes_sb(_nr) Date: Thu, 26 Apr 2012 10:57:43 +0800 Message-ID: <4F98B9A7.8060209@gmail.com> Reply-To: miaoxie1984@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , Linux FSDevel , Linux Btrfs , miaox@cn.fujitsu.com, Kamal Mostafa , Linux Ext4 To: Alexander Viro Return-path: Received: from mail-pz0-f51.google.com ([209.85.210.51]:65426 "EHLO mail-pz0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752358Ab2DZC56 (ORCPT ); Wed, 25 Apr 2012 22:57:58 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: writeback_inodes_sb(_nr) grabs s_umount lock when it want to start writeback, it may bring us deadlock problem when doing umount. So we introduce new functions -- try_to_writeback_inodes_sb(_nr) -- which use down_read_trylock() instead of down_read() to avoid that deadlock problem. This idea came from Christoph Hellwig. Some code is from the patch of Kamal Mostafa. Signed-off-by: Miao Xie --- fs/fs-writeback.c | 39 +++++++++++++++++++++++++++++++++++++++ include/linux/writeback.h | 3 +++ 2 files changed, 42 insertions(+), 0 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 539f36c..b0c35c3 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1291,6 +1291,45 @@ int writeback_inodes_sb_nr_if_idle(struct super_block *sb, EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle); /** + * try_to_writeback_inodes_sb_nr - try to start writeback if none underway + * @sb: the superblock + * @nr: the number of pages to write + * @reason: the reason of writeback + * + * Invoke writeback_inodes_sb_nr if no writeback is currently underway. + * Returns 1 if writeback was started, 0 if not. + */ +int try_to_writeback_inodes_sb_nr(struct super_block *sb, + unsigned long nr, + enum wb_reason reason) +{ + if (writeback_in_progress(sb->s_bdi)) + return 1; + + if (!down_read_trylock(&sb->s_umount)) + return 0; + + writeback_inodes_sb_nr(sb, nr, reason); + up_read(&sb->s_umount); + return 1; +} +EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr); + +/** + * try_to_writeback_inodes_sb - try to start writeback if none underway + * @sb: the superblock + * @reason: reason why some writeback work was initiated + * + * Implement by try_to_writeback_inodes_sb_nr() + * Returns 1 if writeback was started, 0 if not. + */ +int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason) +{ + return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason); +} +EXPORT_SYMBOL(try_to_writeback_inodes_sb); + +/** * sync_inodes_sb - sync sb inode pages * @sb: the superblock * diff --git a/include/linux/writeback.h b/include/linux/writeback.h index a2b84f5..d8e2a99 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -89,6 +89,9 @@ void writeback_inodes_sb_nr(struct super_block *, unsigned long nr, int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason); int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr, enum wb_reason reason); +int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason); +int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr, + enum wb_reason reason); void sync_inodes_sb(struct super_block *); long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages, enum wb_reason reason); -- 1.7.6.5