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Subject[patch 05/32] [PATCH] cio: wait for channel report
From: Sebastian Ott <sebott@linux.vnet.ibm.com>

To fetch a pending channel report word (crw) we use a kernel
thread which triggers stcrw and sleeps on a semaphore. The s390
machine check handler uses crw_handle_channel_report to handle
one crw if needed.

This patch replaces the semaphore with a waitqueue (to block the
kernel thread) and an atomic_t (to count the number of pending
requests).

By this we achieve the ability to force this thread to check for
a pending crw (independent on when it is triggered by the machine
check handler) and wait for this action to finish.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/include/asm/crw.h | 1 +
drivers/s390/cio/crw.c | 29 +++++++++++++++--------------
2 files changed, 16 insertions(+), 14 deletions(-)
Index: quilt-2.6/arch/s390/include/asm/crw.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/crw.h 2010-02-24 09:28:13.000000000 +0100
+++ quilt-2.6/arch/s390/include/asm/crw.h 2010-02-24 09:44:23.000000000 +0100
@@ -32,6 +32,7 @@
extern int crw_register_handler(int rsc, crw_handler_t handler);
extern void crw_unregister_handler(int rsc);
extern void crw_handle_channel_report(void);
+void crw_wait_for_channel_report(void);

#define NR_RSCS 16

Index: quilt-2.6/drivers/s390/cio/crw.c
===================================================================
--- quilt-2.6.orig/drivers/s390/cio/crw.c 2010-02-24 09:28:13.000000000 +0100
+++ quilt-2.6/drivers/s390/cio/crw.c 2010-02-24 09:44:23.000000000 +0100
@@ -8,15 +8,16 @@
* Heiko Carstens <heiko.carstens@de.ibm.com>,
*/

-#include <linux/semaphore.h>
#include <linux/mutex.h>
#include <linux/kthread.h>
#include <linux/init.h>
+#include <linux/wait.h>
#include <asm/crw.h>

-static struct semaphore crw_semaphore;
static DEFINE_MUTEX(crw_handler_mutex);
static crw_handler_t crw_handlers[NR_RSCS];
+static atomic_t crw_nr_req = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(crw_handler_wait_q);

/**
* crw_register_handler() - register a channel report word handler
@@ -59,12 +60,14 @@
static int crw_collect_info(void *unused)
{
struct crw crw[2];
- int ccode;
+ int ccode, signal;
unsigned int chain;
- int ignore;

repeat:
- ignore = down_interruptible(&crw_semaphore);
+ signal = wait_event_interruptible(crw_handler_wait_q,
+ atomic_read(&crw_nr_req) > 0);
+ if (unlikely(signal))
+ atomic_inc(&crw_nr_req);
chain = 0;
while (1) {
crw_handler_t handler;
@@ -122,25 +125,23 @@
/* chain is always 0 or 1 here. */
chain = crw[chain].chn ? chain + 1 : 0;
}
+ if (atomic_dec_and_test(&crw_nr_req))
+ wake_up(&crw_handler_wait_q);
goto repeat;
return 0;
}

void crw_handle_channel_report(void)
{
- up(&crw_semaphore);
+ atomic_inc(&crw_nr_req);
+ wake_up(&crw_handler_wait_q);
}

-/*
- * Separate initcall needed for semaphore initialization since
- * crw_handle_channel_report might be called before crw_machine_check_init.
- */
-static int __init crw_init_semaphore(void)
+void crw_wait_for_channel_report(void)
{
- init_MUTEX_LOCKED(&crw_semaphore);
- return 0;
+ crw_handle_channel_report();
+ wait_event(crw_handler_wait_q, atomic_read(&crw_nr_req) == 0);
}
-pure_initcall(crw_init_semaphore);

/*
* Machine checks for the channel subsystem must be enabled


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