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SubjectRe: race between __sync_single_inode() and iput()/bdev_clear_inode()
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:
>
> ...
> I got the above Oops while doing fs stress test.
>
> The cause of this was race condition between __sync_single_inode() and
> iput()/bdev_clear_inode().
>
> This race seems following condition.
>
> cpu0 (fs's inode) cpu1 (bdev's inode)
> ------------------------------------------------------------------------
> close("/dev/hda2")
> [...]
> __sync_single_inode()
> /* copy the bdev's ->i_mapping */
> mapping = inode->i_mapping;
>
> generic_forget_inode()
> bdev_clear_inode()
> /* restre the fs's ->i_mapping */
> inode->i_mapping = &inode->i_data;
> /* bdev's inode was freed */
> destroy_inode(inode);
>
> if (wait) {
> /* dereference a freed bdev's mapping->host */
> filemap_fdatawait(mapping); /* Oops */
>

The __sync_single_inode() caller takes a ref on the inode to prevent things
like this from happening.

What was the call path on the other process? The one running
destroy_inode()? unmount?

> I wrote the attached patch for making sure fs's inode is not in
> __sync_single_inode().

It would be nicer to honour the extra inode ref in the unmount path, if
poss. Only swizzle i_mapping when the inode is really not in use.

> +/* Called under inode_lock. */
> +void wait_inode_ilock(struct inode *inode)
> +{
> + wait_queue_head_t *wqh;
> + DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK);
> +
> + if (!(inode->i_state & I_LOCK))
> + return;
> +
> + wqh = bit_waitqueue(&inode->i_state, __I_LOCK);
> + do {
> + __iget(inode);
> + spin_unlock(&inode_lock);
> + __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
> + iput(inode);
> + spin_lock(&inode_lock);
> + } while (inode->i_state & I_LOCK);
> +}

Does this differ from wait_on_inode()?

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