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dax: Don't access a freed inode 

After we drop the i_pages lock, the inode can be freed at any time.
The get_unlocked_entry() code has no choice but to reacquire the lock,
so it can't be used here.  Create a new wait_entry_unlocked() which takes
care not to acquire the lock or dereference the address_space in any way.

Fixes: c2a7d2a115 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: <stable@vger.kernel.org>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Matthew Wilcox 2018-11-27 13:16:34 -08:00 committed by Dan Williams
parent c93db7bb6e
commit 55e56f06ed
1 changed files with 29 additions and 3 deletions
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32
fs/dax.c
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@ -232,6 +232,34 @@ static void *get_unlocked_entry(struct xa_state *xas)
}
}
/*
* The only thing keeping the address space around is the i_pages lock
* (it's cycled in clear_inode() after removing the entries from i_pages)
* After we call xas_unlock_irq(), we cannot touch xas->xa.
*/
static void wait_entry_unlocked(struct xa_state *xas, void *entry)
{
struct wait_exceptional_entry_queue ewait;
wait_queue_head_t *wq;
init_wait(&ewait.wait);
ewait.wait.func = wake_exceptional_entry_func;
wq = dax_entry_waitqueue(xas, entry, &ewait.key);
prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
xas_unlock_irq(xas);
schedule();
finish_wait(wq, &ewait.wait);
/*
* Entry lock waits are exclusive. Wake up the next waiter since
* we aren't sure we will acquire the entry lock and thus wake
* the next waiter up on unlock.
*/
if (waitqueue_active(wq))
__wake_up(wq, TASK_NORMAL, 1, &ewait.key);
}
static void put_unlocked_entry(struct xa_state *xas, void *entry)
{
/* If we were the only waiter woken, wake the next one */
@ -389,9 +417,7 @@ bool dax_lock_mapping_entry(struct page *page)
entry = xas_load(&xas);
if (dax_is_locked(entry)) {
rcu_read_unlock();
entry = get_unlocked_entry(&xas);
xas_unlock_irq(&xas);
put_unlocked_entry(&xas, entry);
wait_entry_unlocked(&xas, entry);
rcu_read_lock();
continue;
}