path: root/drivers
diff options
authorSteve Wise <swise@opengridcomputing.com>2011-05-20 16:25:05 +0000
committerRoland Dreier <roland@purestorage.com>2011-05-24 09:47:38 -0700
commitc337374bf23b88620bcc66a7a09f141cc640f548 (patch)
tree5867078d9b9f7e8eb44df4e94b08e460aede1616 /drivers
parent257313b2a87795e07a0bdf58d0fffbdba8b31051 (diff)
RDMA/cxgb4: Use completion objects for event blocking
There exists a race condition when using wait_queue_head_t objects that are declared on the stack. This was being done in a few places where we are sending work requests to the FW and awaiting replies, but we don't have an endpoint structure with an embedded c4iw_wr_wait struct. So the code was allocating it locally on the stack. Bad design. The race is: 1) thread on cpuX declares the wait_queue_head_t on the stack, then posts a firmware WR with that wait object ptr as the cookie to be returned in the WR reply. This thread will proceed to block in wait_event_timeout() but before it does: 2) An interrupt runs on cpuY with the WR reply. fw6_msg() handles this and calls c4iw_wake_up(). c4iw_wake_up() sets the condition variable in the c4iw_wr_wait object to TRUE and will call wake_up(), but before it calls wake_up(): 3) The thread on cpuX calls c4iw_wait_for_reply(), which calls wait_event_timeout(). The wait_event_timeout() macro checks the condition variable and returns immediately since it is TRUE. So this thread never blocks/sleeps. The function then returns effectively deallocating the c4iw_wr_wait object that was on the stack. 4) So at this point cpuY has a pointer to the c4iw_wr_wait object that is no longer valid. Further its pointing to a stack frame that might now be in use by some other context/thread. So cpuY continues execution and calls wake_up() on a ptr to a wait object that as been effectively deallocated. This race, when it hits, can cause a crash in wake_up(), which I've seen under heavy stress. It can also corrupt the referenced stack which can cause any number of failures. The fix: Use struct completion, which supports on-stack declarations. Completions use a spinlock around setting the condition to true and the wake up so that steps 2 and 4 above are atomic and step 3 can never happen in-between. Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Diffstat (limited to 'drivers')
1 files changed, 5 insertions, 13 deletions
diff --git a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
index 35d2a5dd9bb4..4f045375c8e2 100644
--- a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
+++ b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
@@ -35,7 +35,7 @@
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/idr.h>
-#include <linux/workqueue.h>
+#include <linux/completion.h>
#include <linux/netdevice.h>
#include <linux/sched.h>
#include <linux/pci.h>
@@ -131,28 +131,21 @@ static inline int c4iw_num_stags(struct c4iw_rdev *rdev)
#define C4IW_WR_TO (10*HZ)
-enum {
struct c4iw_wr_wait {
- wait_queue_head_t wait;
- unsigned long status;
+ struct completion completion;
int ret;
static inline void c4iw_init_wr_wait(struct c4iw_wr_wait *wr_waitp)
wr_waitp->ret = 0;
- wr_waitp->status = 0;
- init_waitqueue_head(&wr_waitp->wait);
+ init_completion(&wr_waitp->completion);
static inline void c4iw_wake_up(struct c4iw_wr_wait *wr_waitp, int ret)
wr_waitp->ret = ret;
- set_bit(REPLY_READY, &wr_waitp->status);
- wake_up(&wr_waitp->wait);
+ complete(&wr_waitp->completion);
static inline int c4iw_wait_for_reply(struct c4iw_rdev *rdev,
@@ -164,8 +157,7 @@ static inline int c4iw_wait_for_reply(struct c4iw_rdev *rdev,
int ret;
do {
- ret = wait_event_timeout(wr_waitp->wait,
- test_and_clear_bit(REPLY_READY, &wr_waitp->status), to);
+ ret = wait_for_completion_timeout(&wr_waitp->completion, to);
if (!ret) {
printk(KERN_ERR MOD "%s - Device %s not responding - "
"tid %u qpid %u\n", func,

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