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ptr_ring: fix race conditions when resizing 

Resizing currently drops consumer lock.  This can cause entries to be
reordered, which isn't good in itself.  More importantly, consumer can
detect a false ring empty condition and block forever.

Further, nesting of consumer within producer lock is problematic for
tun, since it produces entries in a BH, which causes a lock order
reversal:

       CPU0                    CPU1
       ----                    ----
  consume:
  lock(&(&r->consumer_lock)->rlock);
                               resize:
                               local_irq_disable();
                               lock(&(&r->producer_lock)->rlock);
                               lock(&(&r->consumer_lock)->rlock);
  <Interrupt>
  produce:
  lock(&(&r->producer_lock)->rlock);

To fix, nest producer lock within consumer lock during resize,
and keep consumer lock during the whole swap operation.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
zero-colors
Michael S. Tsirkin 2017-02-19 07:17:17 +02:00 committed by David S. Miller
parent d4e854ccd6
commit e716953071
1 changed files with 31 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
include/linux/ptr_ring.h
View File

@ -111,6 +111,11 @@ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
return 0;
}
/*
* Note: resize (below) nests producer lock within consumer lock, so if you
* consume in interrupt or BH context, you must disable interrupts/BH when
* calling this.
*/
static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
{
int ret;
@ -242,6 +247,11 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
return ptr;
}
/*
* Note: resize (below) nests producer lock within consumer lock, so if you
* call this in interrupt or BH context, you must disable interrupts/BH when
* producing.
*/
static inline void *ptr_ring_consume(struct ptr_ring *r)
{
void *ptr;
@ -357,7 +367,7 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
void **old;
void *ptr;
while ((ptr = ptr_ring_consume(r)))
while ((ptr = __ptr_ring_consume(r)))
if (producer < size)
queue[producer++] = ptr;
else if (destroy)
@ -372,6 +382,12 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
return old;
}
/*
* Note: producer lock is nested within consumer lock, so if you
* resize you must make sure all uses nest correctly.
* In particular if you consume ring in interrupt or BH context, you must
* disable interrupts/BH when doing so.
*/
static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
void (*destroy)(void *))
{
@ -382,17 +398,25 @@ static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
if (!queue)
return -ENOMEM;
spin_lock_irqsave(&(r)->producer_lock, flags);
spin_lock_irqsave(&(r)->consumer_lock, flags);
spin_lock(&(r)->producer_lock);
old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy);
spin_unlock_irqrestore(&(r)->producer_lock, flags);
spin_unlock(&(r)->producer_lock);
spin_unlock_irqrestore(&(r)->consumer_lock, flags);
kfree(old);
return 0;
}
/*
* Note: producer lock is nested within consumer lock, so if you
* resize you must make sure all uses nest correctly.
* In particular if you consume ring in interrupt or BH context, you must
* disable interrupts/BH when doing so.
*/
static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
int size,
gfp_t gfp, void (*destroy)(void *))
@ -412,10 +436,12 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
}
for (i = 0; i < nrings; ++i) {
spin_lock_irqsave(&(rings[i])->producer_lock, flags);
spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
spin_lock(&(rings[i])->producer_lock);
queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
size, gfp, destroy);
spin_unlock_irqrestore(&(rings[i])->producer_lock, flags);
spin_unlock(&(rings[i])->producer_lock);
spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags);
}
for (i = 0; i < nrings; ++i)