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Date: Wed, 20 Jul 2011 16:56:26 -0400
From: Don Zickus <dzickus@...hat.com>
To: tony.luck@...el.com
Cc: LKML <linux-kernel@...r.kernel.org>, ying.huang@...el.com,
Don Zickus <dzickus@...hat.com>
Subject: [PATCH] pstore: change mutex locking to spin_locks
pstore was using mutex locking to protect read/write access to the
backend plug-ins. This causes problems when pstore is executed in
an NMI context through panic() -> kmsg_dump().
This patch changes the mutex to a spin_lock_irqsave then also checks to
see if we are in an NMI context. If we are in an NMI and can't get the
lock, just print a message stating that and blow by the locking.
All this is probably a hack around the bigger locking problem but it
solves my current situation of trying to sleep in an NMI context.
Tested by loading the lkdtm module and executing a HARDLOCKUP which
will cause the machine to panic inside the nmi handler.
Signed-off-by: Don Zickus <dzickus@...hat.com>
---
drivers/acpi/apei/erst.c | 2 +-
fs/pstore/platform.c | 28 ++++++++++++++++++++++------
include/linux/pstore.h | 2 +-
3 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
index e6cef8e..3d9c2a3 100644
--- a/drivers/acpi/apei/erst.c
+++ b/drivers/acpi/apei/erst.c
@@ -1155,7 +1155,7 @@ static int __init erst_init(void)
goto err_release_erange;
buf = kmalloc(erst_erange.size, GFP_KERNEL);
- mutex_init(&erst_info.buf_mutex);
+ spin_lock_init(&erst_info.buf_lock);
if (buf) {
erst_info.buf = buf + sizeof(struct cper_pstore_record);
erst_info.bufsize = erst_erange.size -
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index f2c3ff2..53ba00b 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -27,6 +27,7 @@
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
+#include <linux/hardirq.h>
#include "internal.h"
@@ -68,13 +69,21 @@ static void pstore_dump(struct kmsg_dumper *dumper,
char *dst, *why;
u64 id;
int hsize, part = 1;
+ unsigned long flags = 0;
+ int is_locked = 0;
if (reason < ARRAY_SIZE(reason_str))
why = reason_str[reason];
else
why = "Unknown";
- mutex_lock(&psinfo->buf_mutex);
+ if (in_nmi()) {
+ is_locked = spin_trylock(&psinfo->buf_lock);
+ if (!is_locked)
+ pr_err("pstore dump routine blocked in NMI, may corrupt error record\n");
+ } else {
+ spin_lock_irqsave(&psinfo->buf_lock, flags);
+ }
oopscount++;
while (total < kmsg_bytes) {
dst = psinfo->buf;
@@ -103,7 +112,12 @@ static void pstore_dump(struct kmsg_dumper *dumper,
l2 -= l2_cpy;
total += l1_cpy + l2_cpy;
}
- mutex_unlock(&psinfo->buf_mutex);
+ if (in_nmi()) {
+ if (is_locked)
+ spin_unlock(&psinfo->buf_lock);
+ } else {
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+ }
}
static struct kmsg_dumper pstore_dumper = {
@@ -157,11 +171,12 @@ void pstore_get_records(void)
enum pstore_type_id type;
struct timespec time;
int failed = 0, rc;
+ unsigned long flags;
if (!psi)
return;
- mutex_lock(&psinfo->buf_mutex);
+ spin_lock_irqsave(&psinfo->buf_lock, flags);
rc = psi->open(psi);
if (rc)
goto out;
@@ -173,7 +188,7 @@ void pstore_get_records(void)
}
psi->close(psi);
out:
- mutex_unlock(&psinfo->buf_mutex);
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
if (failed)
printk(KERN_WARNING "pstore: failed to load %d record(s) from '%s'\n",
@@ -187,6 +202,7 @@ out:
int pstore_write(enum pstore_type_id type, char *buf, size_t size)
{
u64 id;
+ unsigned long flags;
if (!psinfo)
return -ENODEV;
@@ -194,13 +210,13 @@ int pstore_write(enum pstore_type_id type, char *buf, size_t size)
if (size > psinfo->bufsize)
return -EFBIG;
- mutex_lock(&psinfo->buf_mutex);
+ spin_lock_irqsave(&psinfo->buf_lock, flags);
memcpy(psinfo->buf, buf, size);
id = psinfo->write(type, size);
if (pstore_is_mounted())
pstore_mkfile(PSTORE_TYPE_DMESG, psinfo->name, id, psinfo->buf,
size, CURRENT_TIME, psinfo->erase);
- mutex_unlock(&psinfo->buf_mutex);
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
return 0;
}
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index 2455ef2..2d77b82 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -32,7 +32,7 @@ enum pstore_type_id {
struct pstore_info {
struct module *owner;
char *name;
- struct mutex buf_mutex; /* serialize access to 'buf' */
+ spinlock_t buf_lock; /* serialize access to 'buf' */
char *buf;
size_t bufsize;
int (*open)(struct pstore_info *psi);
--
1.7.6
--
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