8:16 a.m.
These both fix race conditions in dax_lock_mapping_entry(). I've tagged
them both for 4.19 backport, which will fail and I'll do the equivalent
patch for it. Dan, do you want to take these through your tree?
Matthew Wilcox (2):
dax: Check page->mapping isn't NULL
dax: Don't access a freed inode
fs/dax.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)
--
2.19.1
8:16 a.m.
New subject: [PATCH 1/2] dax: Check page->mapping isn't NULL
If we race with inode destroy, it's possible for page->mapping to be
NULL before we even enter this routine, as well as after having slept
waiting for the dax entry to become unlocked.
Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: stable(a)vger.kernel.org
Reported-by: Jan Kara <jack(a)suse.cz>
Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
---
fs/dax.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/dax.c b/fs/dax.c
index 9bcce89ea18e..e69fc231833b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -365,7 +365,7 @@ bool dax_lock_mapping_entry(struct page *page)
struct address_space *mapping = READ_ONCE(page->mapping);
locked = false;
- if (!dax_mapping(mapping))
+ if (!mapping || !dax_mapping(mapping))
break;
/*
--
2.19.1
8:16 a.m.
New subject: [PATCH 2/2] 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: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: stable(a)vger.kernel.org
Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
---
fs/dax.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index e69fc231833b..cf1805645d18 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -232,6 +232,28 @@ 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);
+ 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 +411,7 @@ 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;
}
--
2.19.1
8:18 p.m.
New subject: [PATCH 1/2] dax: Check page->mapping isn't NULL
Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn(a)suse.de>
--
Johannes Thumshirn SUSE Labs
jthumshirn(a)suse.de +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850
10:46 p.m.
New subject: [PATCH 1/2] dax: Check page->mapping isn't NULL
On Tue 27-11-18 13:16:33, Matthew Wilcox wrote:
If we race with inode destroy, it's possible for page->mapping
to be
NULL before we even enter this routine, as well as after having slept
waiting for the dax entry to become unlocked.
Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Cc: stable(a)vger.kernel.org
Reported-by: Jan Kara <jack(a)suse.cz>
Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
Thanks for writing this fix. The patch looks good. You can add:
Reviewed-by: Jan Kara <jack(a)suse.cz>
Honza
---
fs/dax.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/dax.c b/fs/dax.c
index 9bcce89ea18e..e69fc231833b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -365,7 +365,7 @@ bool dax_lock_mapping_entry(struct page *page)
struct address_space *mapping = READ_ONCE(page->mapping);
locked = false;
- if (!dax_mapping(mapping))
+ if (!mapping || !dax_mapping(mapping))
break;
/*
--
2.19.1
--
Jan Kara <jack(a)suse.com>
SUSE Labs, CR
10:53 p.m.
New subject: [PATCH 2/2] dax: Don't access a freed inode
On Tue 27-11-18 13:16:34, Matthew Wilcox wrote:
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: stable(a)vger.kernel.org
Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack(a)suse.cz>
Just one nit below:
+/*
+ * 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);
Can we add a comment here like:
/*
* 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.
*/
Because I always wonder for a moment why this is needed.
+ if (waitqueue_active(wq))
+ __wake_up(wq, TASK_NORMAL, 1, &ewait.key);
+}
+
Honza
--
Jan Kara <jack(a)suse.com>
SUSE Labs, CR
4:08 a.m.
New subject: [PATCH 2/2] dax: Don't access a freed inode
On Wed, Nov 28, 2018 at 3:54 AM Jan Kara <jack(a)suse.cz> wrote:
On Tue 27-11-18 13:16:34, Matthew Wilcox wrote:
> 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: stable(a)vger.kernel.org
> Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack(a)suse.cz>
Just one nit below:
> +/*
> + * 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);
Can we add a comment here like:
/*
* 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.
*/
Because I always wonder for a moment why this is needed.
Looks good, I'll add that when applying.
4:10 a.m.
New subject: [PATCH 2/2] dax: Don't access a freed inode
On Wed, Nov 28, 2018 at 09:08:40AM -0800, Dan Williams wrote:
> Can we add a comment here like:
>
> /*
> * 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.
> */
>
> Because I always wonder for a moment why this is needed.
Looks good, I'll add that when applying.
Thanks.
6:44 a.m.
New subject: [PATCH v2] dax: Don't access a freed inode
From: Matthew Wilcox <willy(a)infradead.org>
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: <stable(a)vger.kernel.org>
Signed-off-by: Matthew Wilcox <willy(a)infradead.org>
Reviewed-by: Jan Kara <jack(a)suse.cz>
Signed-off-by: Dan Williams <dan.j.williams(a)intel.com>
---
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;
}
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8 comments
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Matthew Wilcox