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@redhat.com>
Acked-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index ca60ebc..0472924 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -28,6 +28,7 @@
#include <linux/timer.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
+#include <linux/hardirq.h>
#include <linux/workqueue.h>
#include "internal.h"
@@ -88,13 +89,20 @@
u64 id;
int hsize;
unsigned int 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;
@@ -123,7 +131,11 @@
total += l1_cpy + l2_cpy;
part++;
}
- 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 = {
@@ -188,11 +200,12 @@
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;
@@ -205,7 +218,7 @@
}
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",
@@ -233,7 +246,8 @@
*/
int pstore_write(enum pstore_type_id type, char *buf, size_t size)
{
- u64 id;
+ u64 id;
+ unsigned long flags;
if (!psinfo)
return -ENODEV;
@@ -241,13 +255,13 @@
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, 0, size, psinfo);
if (pstore_is_mounted())
pstore_mkfile(PSTORE_TYPE_DMESG, psinfo->name, id, psinfo->buf,
size, CURRENT_TIME, psinfo);
- mutex_unlock(&psinfo->buf_mutex);
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
return 0;
}