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nilfs2: correct exclusion control in nilfs_remount function

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nilfs_remount() changes mount state of a superblock instance.  Even
though nilfs accesses other superblock instances during mount or
remount, the mount state was not properly protected in
nilfs_remount().

Moreover, nilfs_remount() has a lock order reversal problem;
nilfs_get_sb() holds:

  1. bdev->bd_mount_sem
  2. sb->s_umount  (sget acquires)

and nilfs_remount() holds:

  1. sb->s_umount  (locked by the caller in vfs)
  2. bdev->bd_mount_sem

To avoid these problems, this patch divides a semaphore protecting
super block instances from nilfs->ns_sem, and applies it to the mount
state protection in nilfs_remount().

With this change, bd_mount_sem use is removed from nilfs_remount() and
the lock order reversal will be resolved.  And the new rw-semaphore,
nilfs->ns_super_sem will properly protect the mount state except the
modification from nilfs_error function.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Ryusuke Konishi
2009-06-08 01:39:32 +09:00
committad av Al Viro
förälder 6dd4740662
incheckning e59399d010
3 ändrade filer med 33 tillägg och 31 borttagningar
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7
fs/nilfs2/the_nilfs.h
Visa fil

@@ -48,6 +48,7 @@ enum {
* @ns_bdi: backing dev info
* @ns_writer: back pointer to writable nilfs_sb_info
* @ns_sem: semaphore for shared states
* @ns_super_sem: semaphore for global operations across super block instances
* @ns_writer_mutex: mutex protecting ns_writer attach/detach
* @ns_writer_refcount: number of referrers on ns_writer
* @ns_current: back pointer to current mount
@@ -96,10 +97,15 @@ struct the_nilfs {
struct backing_dev_info *ns_bdi;
struct nilfs_sb_info *ns_writer;
struct rw_semaphore ns_sem;
struct rw_semaphore ns_super_sem;
struct mutex ns_writer_mutex;
atomic_t ns_writer_refcount;
/*
* components protected by ns_super_sem
*/
struct nilfs_sb_info *ns_current;
struct list_head ns_supers;
/*
* used for
@@ -113,7 +119,6 @@ struct the_nilfs {
time_t ns_sbwtime[2];
unsigned ns_sbsize;
unsigned ns_mount_state;
struct list_head ns_supers;
/*
* Following fields are dedicated to a writable FS-instance.