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authorMiklos Szeredi <mszeredi@suse.cz>2011-11-21 12:11:31 +0100
committerAl Viro <viro@zeniv.linux.org.uk>2012-01-06 23:20:12 -0500
commit4ed5e82fe77f4147cf386327c9a63a2dd7eff518 (patch)
treef4eaeefaf5d293014457892ac31f878eece07331 /COPYING
parent39f7c4db1d2d9e2e2a90abdf34811783089d217d (diff)
vfs: protect remounting superblock read-only
Currently remouting superblock read-only is racy in a major way. With the per mount read-only infrastructure it is now possible to prevent most races, which this patch attempts. Before starting the remount read-only, iterate through all mounts belonging to the superblock and if none of them have any pending writes, set sb->s_readonly_remount. This indicates that remount is in progress and no further write requests are allowed. If the remount succeeds set MS_RDONLY and reset s_readonly_remount. If the remounting is unsuccessful just reset s_readonly_remount. This can result in transient EROFS errors, despite the fact the remount failed. Unfortunately hodling off writes is difficult as remount itself may touch the filesystem (e.g. through load_nls()) which would deadlock. A later patch deals with delayed writes due to nlink going to zero. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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