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Patch "ptr_ring: fix race conditions when resizing" has been added to the 4.9-stable tree

PATCH [email protected] 1 participant 1 message Feb 23, 2017 Stable branch

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This is a note to let you know that I've just added the patch titled

ptr_ring: fix race conditions when resizing

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ptr_ring-fix-race-conditions-when-resizing.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Thu Feb 23 21:13:05 CET 2017

From: "Michael S. Tsirkin" <[email protected]>
Date: Sun, 19 Feb 2017 07:17:17 +0200
Subject: ptr_ring: fix race conditions when resizing

From: "Michael S. Tsirkin" <[email protected]>

[ Upstream commit e71695307114335be1ed912f4a347396c2ed0e69 ]

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 <[email protected]>
Cc [email protected]
Cc "David S. Miller" <[email protected]>
Acked-by Jason Wang <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>
Signed-off-by David S. Miller <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 include/linux/ptr_ring.h |   36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)
include/linux/ptr_ring.h +31 -5
@@ -111,6 +111,11 @@ static inline int __ptr_ring_produce(str
 	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(s
 	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_que
 	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_que
 	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
 	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_multip
 	}
 
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ptr_ring-fix-race-conditions-when-resizing.patch