[ 3.8.y.z extended stable ] Patch "[SCSI] zfcp: fix lock imbalance by reworking request queue locking" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Thu Aug 29 23:47:23 UTC 2013
This is a note to let you know that I have just added a patch titled
[SCSI] zfcp: fix lock imbalance by reworking request queue locking
to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue
This patch is scheduled to be released in version 3.8.13.8.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From f5e7ca460127c5c7a5edaf2e9966a81e23378bfa Mon Sep 17 00:00:00 2001
From: Martin Peschke <mpeschke at linux.vnet.ibm.com>
Date: Thu, 22 Aug 2013 17:45:36 +0200
Subject: [SCSI] zfcp: fix lock imbalance by reworking request queue locking
commit d79ff142624e1be080ad8d09101f7004d79c36e1 upstream.
This patch adds wait_event_interruptible_lock_irq_timeout(), which is a
straight-forward descendant of wait_event_interruptible_timeout() and
wait_event_interruptible_lock_irq().
The zfcp driver used to call wait_event_interruptible_timeout()
in combination with some intricate and error-prone locking. Using
wait_event_interruptible_lock_irq_timeout() as a replacement
nicely cleans up that locking.
This rework removes a situation that resulted in a locking imbalance
in zfcp_qdio_sbal_get():
BUG: workqueue leaked lock or atomic: events/1/0xffffff00/10
last function: zfcp_fc_wka_port_offline+0x0/0xa0 [zfcp]
It was introduced by commit c2af7545aaff3495d9bf9a7608c52f0af86fb194
"[SCSI] zfcp: Do not wait for SBALs on stopped queue", which had a new
code path related to ZFCP_STATUS_ADAPTER_QDIOUP that took an early exit
without a required lock being held. The problem occured when a
special, non-SCSI I/O request was being submitted in process context,
when the adapter's queues had been torn down. In this case the bug
surfaced when the Fibre Channel port connection for a well-known address
was closed during a concurrent adapter shut-down procedure, which is a
rare constellation.
This patch also fixes these warnings from the sparse tool (make C=1):
drivers/s390/scsi/zfcp_qdio.c:224:12: warning: context imbalance in
'zfcp_qdio_sbal_check' - wrong count at exit
drivers/s390/scsi/zfcp_qdio.c:244:5: warning: context imbalance in
'zfcp_qdio_sbal_get' - unexpected unlock
Last but not least, we get rid of that crappy lock-unlock-lock
sequence at the beginning of the critical section.
It is okay to call zfcp_erp_adapter_reopen() with req_q_lock held.
Reported-by: Mikulas Patocka <mpatocka at redhat.com>
Reported-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Signed-off-by: Martin Peschke <mpeschke at linux.vnet.ibm.com>
Signed-off-by: Steffen Maier <maier at linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley at Parallels.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
drivers/s390/scsi/zfcp_qdio.c | 8 ++----
include/linux/wait.h | 57 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 59 insertions(+), 6 deletions(-)
diff --git a/drivers/s390/scsi/zfcp_qdio.c b/drivers/s390/scsi/zfcp_qdio.c
index 50b5615..925fb1f 100644
--- a/drivers/s390/scsi/zfcp_qdio.c
+++ b/drivers/s390/scsi/zfcp_qdio.c
@@ -224,11 +224,9 @@ int zfcp_qdio_sbals_from_sg(struct zfcp_qdio *qdio, struct zfcp_qdio_req *q_req,
static int zfcp_qdio_sbal_check(struct zfcp_qdio *qdio)
{
- spin_lock_irq(&qdio->req_q_lock);
if (atomic_read(&qdio->req_q_free) ||
!(atomic_read(&qdio->adapter->status) & ZFCP_STATUS_ADAPTER_QDIOUP))
return 1;
- spin_unlock_irq(&qdio->req_q_lock);
return 0;
}
@@ -246,9 +244,8 @@ int zfcp_qdio_sbal_get(struct zfcp_qdio *qdio)
{
long ret;
- spin_unlock_irq(&qdio->req_q_lock);
- ret = wait_event_interruptible_timeout(qdio->req_q_wq,
- zfcp_qdio_sbal_check(qdio), 5 * HZ);
+ ret = wait_event_interruptible_lock_irq_timeout(qdio->req_q_wq,
+ zfcp_qdio_sbal_check(qdio), qdio->req_q_lock, 5 * HZ);
if (!(atomic_read(&qdio->adapter->status) & ZFCP_STATUS_ADAPTER_QDIOUP))
return -EIO;
@@ -262,7 +259,6 @@ int zfcp_qdio_sbal_get(struct zfcp_qdio *qdio)
zfcp_erp_adapter_reopen(qdio->adapter, 0, "qdsbg_1");
}
- spin_lock_irq(&qdio->req_q_lock);
return -EIO;
}
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 30194a6..7c7eead 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -719,6 +719,63 @@ do { \
__ret; \
})
+#define __wait_event_interruptible_lock_irq_timeout(wq, condition, \
+ lock, ret) \
+do { \
+ DEFINE_WAIT(__wait); \
+ \
+ for (;;) { \
+ prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
+ if (condition) \
+ break; \
+ if (signal_pending(current)) { \
+ ret = -ERESTARTSYS; \
+ break; \
+ } \
+ spin_unlock_irq(&lock); \
+ ret = schedule_timeout(ret); \
+ spin_lock_irq(&lock); \
+ if (!ret) \
+ break; \
+ } \
+ finish_wait(&wq, &__wait); \
+} while (0)
+
+/**
+ * wait_event_interruptible_lock_irq_timeout - sleep until a condition gets true or a timeout elapses.
+ * The condition is checked under the lock. This is expected
+ * to be called with the lock taken.
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ * @lock: a locked spinlock_t, which will be released before schedule()
+ * and reacquired afterwards.
+ * @timeout: timeout, in jiffies
+ *
+ * The process is put to sleep (TASK_INTERRUPTIBLE) until the
+ * @condition evaluates to true or signal is received. The @condition is
+ * checked each time the waitqueue @wq is woken up.
+ *
+ * wake_up() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * This is supposed to be called while holding the lock. The lock is
+ * dropped before going to sleep and is reacquired afterwards.
+ *
+ * The function returns 0 if the @timeout elapsed, -ERESTARTSYS if it
+ * was interrupted by a signal, and the remaining jiffies otherwise
+ * if the condition evaluated to true before the timeout elapsed.
+ */
+#define wait_event_interruptible_lock_irq_timeout(wq, condition, lock, \
+ timeout) \
+({ \
+ int __ret = timeout; \
+ \
+ if (!(condition)) \
+ __wait_event_interruptible_lock_irq_timeout( \
+ wq, condition, lock, __ret); \
+ __ret; \
+})
+
/*
* These are the old interfaces to sleep waiting for an event.
--
1.8.1.2
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