Re: [RFC, PATCH] filesystem freeze: fix sys_umount induced perpetual freeze

From: Christoph Hellwig
Date: Wed Aug 26 2009 - 13:39:13 EST

On Wed, Aug 26, 2009 at 02:00:01PM +0900, Fernando Luis V??zquez Cao wrote:
> The current locking scheme for filesystem freeze avoids races between
> freeze_bdev() and do_umount() by taking the s_umount semaphore.
> If freeze_bdev() wins the race the process that invoked sys_umount
> will sleep until thaw_bdev releases the semaphore. Unfortunately, this
> will never happen because thaw_bdev bails out early the
> bd_fsfreeze_count check having failed (the count is 0).
> The problem is that the block_device that ioctl_fsthaw() passes to
> thaw_bdev() is not the one that we freezed because before sleeping in
> deactivate_super() do_umount() released the dentry (dput()) and freed
> the vfs mount (free_vfsmnt()).
> This patch works around this issue by checking the freeze level in
> do_umount()

This should be solved my my freeze locking rewrite:

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