[PATCH repost] ptr_ring: fix race conditions when resizing
DORMANTno replies
REVIEWED: 1 (0M)
From: Michael S. Tsirkin <mst@redhat.com>
Date: 2017-02-19 05:17:19
Subsystem:
the rest · Maintainer:
Linus Torvalds
Status: Reviewed.
1 review trailer.
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: <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: Jason Wang <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
Dave, could you merge this before 4.10? If not - I can try.
include/linux/ptr_ring.h | 36 +++++++++++++++++++++++++++++++-----
1 file changed, 31 insertions(+), 5 deletions(-)
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 2052011..6c70444 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h@@ -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)
--
MST