backing-dev: ensure that a removed bdi no longer has super_block referencing it (592b09a4) · Commits · e / devices / android_kernel_xiaomi_markw

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>

mm/backing-dev.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -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++)