From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH v2] dax: Don't access a freed inode From: Dan Williams To: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org, Matthew Wilcox , Jan Kara , stable@vger.kernel.org, linux-nvdimm@lists.01.org Date: Wed, 28 Nov 2018 11:44:07 -0800 Message-ID: <154343424782.982643.12596428619928518745.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <20181127211634.4995-3-willy@infradead.org> References: <20181127211634.4995-3-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: From: Matthew Wilcox 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: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()") Cc: Signed-off-by: Matthew Wilcox Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/dax.c | 32 +++++++++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index e69fc231833b..3f592dc18d67 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -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; }