linux-kernel - what lock protects sb->s

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Message-ID: <4548639C.7070608@sw.ru>
Date:	Wed, 01 Nov 2006 12:06:36 +0300
From:	Vasily Averin <vvs@...ru>
To:	akpm@...l.org
CC:	viro@...iv.linux.org.uk, devel@...nvz.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: what lock protects sb->s_flags

akpm@...l.org wrote:
> Subject: VFS: BKL is not required for remount_fs()
> 
> According to Documentation/filesystems/Locking remount_fs() does not
> require BKL.
> 
> (akpm: what lock _does_ protect sb->s_flags?)

In general s_flags is changed under sb->s_umount (write) semaphore
inside various get_sb(), fill_super() and remount_fs() filesystem functions.
Exceptions are:
1) do_emergency_remount -- where s_umount(read) is taken,
2) various filesystem error-handlers (like ext3_abort() and reiserfs_abort()),
when filesystem "remounted" to read-only without any locks.

Thank you,
	Vasily Averin
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