Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752300AbXBERdy (ORCPT ); Mon, 5 Feb 2007 12:33:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752388AbXBERdy (ORCPT ); Mon, 5 Feb 2007 12:33:54 -0500 Received: from verein.lst.de ([213.95.11.210]:35548 "EHLO mail.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752249AbXBERdx (ORCPT ); Mon, 5 Feb 2007 12:33:53 -0500 Date: Mon, 5 Feb 2007 18:32:47 +0100 From: Christoph Hellwig To: akpm@osdl.org, haveblue@us.ibm.com Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH[RFC] kill sysrq-u (emergency remount r/o) Message-ID: <20070205173247.GA25790@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.28i X-Spam-Score: -0.001 () BAYES_44 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5880 Lines: 190 Hi there, in two recent discussions (file_list_lock scalability and remount r/o on suspend) I stumbled over this emergency remount feature. It's not actually useful because it tries a potentially dangerous remount despite writers still beeing in progress, which we can't get rid. I've attached one patch in this mail that simply kills the functionality, and in a reply to this mail I'll send a second one that keeps the sysrq functionality, but removes the force argument from do_remount_sb that overrides the still busy check. This version is currently not useful, but makes a lot of sense once Dave Hansens per-mountpoint r/o patches get in, as we can check for a real write in progress instead of simply a file opened with write permission. Any ideas and comments? Index: linux-2.6/drivers/char/sysrq.c =================================================================== --- linux-2.6.orig/drivers/char/sysrq.c 2007-02-05 18:05:11.000000000 +0100 +++ linux-2.6/drivers/char/sysrq.c 2007-02-05 18:12:47.000000000 +0100 @@ -159,17 +159,6 @@ .enable_mask = SYSRQ_ENABLE_SYNC, }; -static void sysrq_handle_mountro(int key, struct tty_struct *tty) -{ - emergency_remount(); -} -static struct sysrq_key_op sysrq_mountro_op = { - .handler = sysrq_handle_mountro, - .help_msg = "Unmount", - .action_msg = "Emergency Remount R/O", - .enable_mask = SYSRQ_ENABLE_REMOUNT, -}; - #ifdef CONFIG_LOCKDEP static void sysrq_handle_showlocks(int key, struct tty_struct *tty) { @@ -340,7 +329,7 @@ &sysrq_unraw_op, /* r */ &sysrq_sync_op, /* s */ &sysrq_showstate_op, /* t */ - &sysrq_mountro_op, /* u */ + NULL, /* u */ /* v: May be registered at init time by SMP VOYAGER */ NULL, /* v */ &sysrq_showstate_blocked_op, /* w */ Index: linux-2.6/fs/namespace.c =================================================================== --- linux-2.6.orig/fs/namespace.c 2007-02-05 18:03:23.000000000 +0100 +++ linux-2.6/fs/namespace.c 2007-02-05 18:04:24.000000000 +0100 @@ -597,7 +597,7 @@ if (!(sb->s_flags & MS_RDONLY)) { lock_kernel(); DQUOT_OFF(sb); - retval = do_remount_sb(sb, MS_RDONLY, NULL, 0); + retval = do_remount_sb(sb, MS_RDONLY, NULL); unlock_kernel(); } up_write(&sb->s_umount); @@ -964,7 +964,7 @@ return -EINVAL; down_write(&sb->s_umount); - err = do_remount_sb(sb, flags, data, 0); + err = do_remount_sb(sb, flags, data); if (!err) nd->mnt->mnt_flags = mnt_flags; up_write(&sb->s_umount); Index: linux-2.6/fs/super.c =================================================================== --- linux-2.6.orig/fs/super.c 2007-02-05 18:03:23.000000000 +0100 +++ linux-2.6/fs/super.c 2007-02-05 18:04:54.000000000 +0100 @@ -557,35 +557,14 @@ } /** - * mark_files_ro - * @sb: superblock in question - * - * All files are marked read/only. We don't care about pending - * delete files so this should be used in 'force' mode only - */ - -static void mark_files_ro(struct super_block *sb) -{ - struct file *f; - - file_list_lock(); - list_for_each_entry(f, &sb->s_files, f_u.fu_list) { - if (S_ISREG(f->f_path.dentry->d_inode->i_mode) && file_count(f)) - f->f_mode &= ~FMODE_WRITE; - } - file_list_unlock(); -} - -/** * do_remount_sb - asks filesystem to change mount options. * @sb: superblock in question * @flags: numeric part of options * @data: the rest of options - * @force: whether or not to force the change * * Alters the mount options of a mounted file system. */ -int do_remount_sb(struct super_block *sb, int flags, void *data, int force) +int do_remount_sb(struct super_block *sb, int flags, void *data) { int retval; @@ -601,9 +580,7 @@ /* If we are remounting RDONLY and current sb is read/write, make sure there are no rw files opened */ if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) { - if (force) - mark_files_ro(sb); - else if (!fs_may_remount_ro(sb)) + if (!fs_may_remount_ro(sb)) return -EBUSY; } @@ -618,37 +595,6 @@ return 0; } -static void do_emergency_remount(unsigned long foo) -{ - struct super_block *sb; - - spin_lock(&sb_lock); - list_for_each_entry(sb, &super_blocks, s_list) { - sb->s_count++; - spin_unlock(&sb_lock); - down_read(&sb->s_umount); - if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) { - /* - * ->remount_fs needs lock_kernel(). - * - * What lock protects sb->s_flags?? - */ - lock_kernel(); - do_remount_sb(sb, MS_RDONLY, NULL, 1); - unlock_kernel(); - } - drop_super(sb); - spin_lock(&sb_lock); - } - spin_unlock(&sb_lock); - printk("Emergency Remount complete\n"); -} - -void emergency_remount(void) -{ - pdflush_operation(do_emergency_remount, 0); -} - /* * Unnamed block devices are dummy devices used by virtual * filesystems which don't use real block-devices. -- jrs @@ -861,7 +807,7 @@ } s->s_flags |= MS_ACTIVE; } - do_remount_sb(s, flags, data, 0); + do_remount_sb(s, flags, data); return simple_set_mnt(mnt, s); } Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h 2007-02-05 18:03:23.000000000 +0100 +++ linux-2.6/include/linux/fs.h 2007-02-05 18:05:16.000000000 +0100 @@ -1599,9 +1599,7 @@ extern void sync_filesystems(int wait); extern void __fsync_super(struct super_block *sb); extern void emergency_sync(void); -extern void emergency_remount(void); -extern int do_remount_sb(struct super_block *sb, int flags, - void *data, int force); +extern int do_remount_sb(struct super_block *sb, int flags, void *data); #ifdef CONFIG_BLOCK extern sector_t bmap(struct inode *, sector_t); #endif - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/