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Message-Id: <E1JwiZa-0007UA-Tm@pomaz-ex.szeredi.hu>
Date: Thu, 15 May 2008 20:53:02 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: ajones@...erbed.com
CC: a.p.zijlstra@...llo.nl, mszeredi@...e.cz,
akpm@...ux-foundation.org, kay.sievers@...y.org, greg@...ah.com,
trond.myklebust@....uio.no, torvalds@...ux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [BUG] mm: bdi: export BDI attributes in sysfs
> About 1 in 4 times, when turning the power back
> on for a drive, I get the BUG reported below. The
> drives are not mounted, just sitting there getting
> power cycled (the test looks to make sure they are
> being seen by the scsi subsystem and udev).
> > BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000000
> > IP: [<ffffffff802694e3>] read_ahead_kb_show+0x1b/0x2d
I suspect this is because there's a race between the show/store
functions and dev_set_drvdata() in bdi_register().
Could you try this patch to verify that this is indeed the problem?
This is not meant as a final solution, I'm sure Greg or Kay can help
find a better solution.
Thanks,
Miklos
Index: linux-2.6/mm/backing-dev.c
===================================================================
--- linux-2.6.orig/mm/backing-dev.c 2008-05-14 12:49:33.000000000 +0200
+++ linux-2.6/mm/backing-dev.c 2008-05-15 20:37:55.000000000 +0200
@@ -15,6 +15,7 @@ static struct class *bdi_class;
#include <linux/seq_file.h>
static struct dentry *bdi_debug_root;
+static DEFINE_MUTEX(bdi_dev_mutex);
static void bdi_debug_init(void)
{
@@ -84,11 +85,19 @@ static inline void bdi_debug_unregister(
}
#endif
+static struct backing_dev_info *dev_get_bdi(struct device *dev)
+{
+ mutex_lock(&bdi_dev_mutex);
+ mutex_unlock(&bdi_dev_mutex);
+
+ return dev_get_drvdata(dev);
+}
+
static ssize_t read_ahead_kb_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
- struct backing_dev_info *bdi = dev_get_drvdata(dev);
+ struct backing_dev_info *bdi = dev_get_bdi(dev);
char *end;
unsigned long read_ahead_kb;
ssize_t ret = -EINVAL;
@@ -107,7 +116,7 @@ static ssize_t read_ahead_kb_store(struc
static ssize_t name##_show(struct device *dev, \
struct device_attribute *attr, char *page) \
{ \
- struct backing_dev_info *bdi = dev_get_drvdata(dev); \
+ struct backing_dev_info *bdi = dev_get_bdi(dev); \
\
return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
}
@@ -117,7 +126,7 @@ BDI_SHOW(read_ahead_kb, K(bdi->ra_pages)
static ssize_t min_ratio_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
- struct backing_dev_info *bdi = dev_get_drvdata(dev);
+ struct backing_dev_info *bdi = dev_get_bdi(dev);
char *end;
unsigned int ratio;
ssize_t ret = -EINVAL;
@@ -135,7 +144,7 @@ BDI_SHOW(min_ratio, bdi->min_ratio)
static ssize_t max_ratio_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
- struct backing_dev_info *bdi = dev_get_drvdata(dev);
+ struct backing_dev_info *bdi = dev_get_bdi(dev);
char *end;
unsigned int ratio;
ssize_t ret = -EINVAL;
@@ -184,6 +193,7 @@ int bdi_register(struct backing_dev_info
if (!name)
return -ENOMEM;
+ mutex_lock(&bdi_dev_mutex);
dev = device_create(bdi_class, parent, MKDEV(0, 0), name);
if (IS_ERR(dev)) {
ret = PTR_ERR(dev);
@@ -195,6 +205,7 @@ int bdi_register(struct backing_dev_info
bdi_debug_register(bdi, name);
exit:
+ mutex_unlock(&bdi_dev_mutex);
kfree(name);
return ret;
}
--
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