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Message-Id: <1377097531-4942-5-git-send-email-maier@linux.vnet.ibm.com>
Date: Wed, 21 Aug 2013 17:05:27 +0200
From: Steffen Maier <maier@...ux.vnet.ibm.com>
To: James Bottomley <James.Bottomley@...senPartnership.com>
Cc: linux-scsi@...r.kernel.org, linux-s390@...r.kernel.org,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Steffen Maier <maier@...ux.vnet.ibm.com>,
Martin Peschke <mpeschke@...ux.vnet.ibm.com>,
stable@...r.kernel.org.#2.6.35+,
Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
Jens Axboe <axboe@...nel.dk>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
linux-kernel@...r.kernel.org
Subject: [PATCH 4/8] zfcp: fix lock imbalance by reworking request queue locking
From: Martin Peschke <mpeschke@...ux.vnet.ibm.com>
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@...hat.com>
Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Martin Peschke <mpeschke@...ux.vnet.ibm.com>
Cc: stable@...r.kernel.org #2.6.35+
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Howells <dhowells@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Steffen Maier <maier@...ux.vnet.ibm.com>
---
drivers/s390/scsi/zfcp_qdio.c | 8 +----
include/linux/wait.h | 57 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 59 insertions(+), 6 deletions(-)
--- 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_
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
{
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
zfcp_erp_adapter_reopen(qdio->adapter, 0, "qdsbg_1");
}
- spin_lock_irq(&qdio->req_q_lock);
return -EIO;
}
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -811,6 +811,63 @@ 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.
--
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