[PATCH 3/4] mtdoops: Ensure sequential write to the buffer

Richard Purdie
2008-01-29T11:27:48Z

>From a5ef8a78b4214f5efcc7310e71dd1e351672af3f Mon Sep 17 00:00:00 2001
From: Richard Purdie <rpurdie@rpsys.net>
Date: Tue, 29 Jan 2008 10:21:56 +0000
Subject: [PATCH] [MTD] mtdoops: Ensure sequential write to the buffer

Add a spinlock to ensure writes to the mtdoops buffer memory are
sequential and don't race.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
---
drivers/mtd/mtdoops.c | 28 ++++++++++++++++++++++++++++
1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 72c434c..1687521 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -28,6 +28,7 @@
#include <linux/workqueue.h>
#include <linux/sched.h>
#include <linux/wait.h>
+#include <linux/spinlock.h>
#include <linux/mtd/mtd.h>

#define OOPS_PAGE_SIZE 4096
@@ -42,6 +43,9 @@ struct mtdoops_context {
int nextcount;

void *oops_buf;
+
+ /* writecount and disabling ready are spin lock protected */
+ spinlock_t writecount_lock;
int ready;
int writecount;
} oops_cxt;
@@ -290,11 +294,22 @@ static void mtdoops_console_sync(void)
{
struct mtdoops_context *cxt = &oops_cxt;
struct mtd_info *mtd = cxt->mtd;
+ unsigned long flags;

if (!cxt->ready || !mtd || cxt->writecount == 0)
return;

+ /*
+ * Once ready is 0 and we've held the lock no further writes to the
+ * buffer will happen
+ */
+ spin_lock_irqsave(&cxt->writecount_lock, flags);
+ if (!cxt->ready) {
+ spin_unlock_irqrestore(&cxt->writecount_lock, flags);
+ return;
+ }
cxt->ready = 0;
+ spin_unlock_irqrestore(&cxt->writecount_lock, flags);

schedule_work(&cxt->work_write);
}
@@ -304,6 +319,7 @@ mtdoops_console_write(struct console *co, const char *s, unsigned int count)
{
struct mtdoops_context *cxt = co->data;
struct mtd_info *mtd = cxt->mtd;
+ unsigned long flags;

if (!oops_in_progress) {
mtdoops_console_sync();
@@ -313,6 +329,13 @@ mtdoops_console_write(struct console *co, const char *s, unsigned int count)
if (!cxt->ready || !mtd)
return;

+ /* Locking on writecount ensures sequential writes to the buffer */
+ spin_lock_irqsave(&cxt->writecount_lock, flags);
+
+ /* Check ready status didn't change whilst waiting for the lock */
+ if (!cxt->ready)
+ return;
+
if (cxt->writecount == 0) {
u32 *stamp = cxt->oops_buf;
*stamp = cxt->nextcount;
@@ -324,6 +347,11 @@ mtdoops_console_write(struct console *co, const char *s, unsigned int count)

memcpy(cxt->oops_buf + cxt->writecount, s, count);
cxt->writecount += count;
+
+ spin_unlock_irqrestore(&cxt->writecount_lock, flags);
+
+ if (cxt->writecount == OOPS_PAGE_SIZE)
+ mtdoops_console_sync();
}

static int __init mtdoops_console_setup(struct console *co, char *options)
--
1.5.2.3