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backing-dev: ensure that a removed bdi no longer has super_block referencing it

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When the bdi is being removed, we have to ensure that no super_blocks
currently have that cached in sb->s_bdi. Normally this is ensured by
the sb having a longer life span than the bdi, but if the device is
suddenly yanked, we have to kill this reference. sb->s_bdi is pointed
to freed memory at that point.

This fixes a problem with sync(1) hanging when a USB stick is pulled
without cleanly umounting it first.

Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2009-10-29 11:46:12 +01:00
parent 960cc0f4fe
commit 592b09a42f
1 changed files with 16 additions and 0 deletions
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16
mm/backing-dev.c
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@ -610,6 +610,21 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
kthread_stop(wb->task);
}
/*
* This bdi is going away now, make sure that no super_blocks point to it
*/
static void bdi_prune_sb(struct backing_dev_info *bdi)
{
struct super_block *sb;
spin_lock(&sb_lock);
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_bdi == bdi)
sb->s_bdi = NULL;
}
spin_unlock(&sb_lock);
}
void bdi_unregister(struct backing_dev_info *bdi)
{
if (bdi->dev) {
@ -682,6 +697,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
spin_unlock(&inode_lock);
}
bdi_prune_sb(bdi);
bdi_unregister(bdi);
for (i = 0; i < NR_BDI_STAT_ITEMS; i++)