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>

1 files changed, 21 insertions, 7 deletions

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index ca60ebcfb15f..0472924024cc 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 @@ static void pstore_dump(struct kmsg_dumper *dumper,
         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 @@ static void pstore_dump(struct kmsg_dumper *dumper,
                 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 @@ void pstore_get_records(int quiet)
         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 @@ void pstore_get_records(int quiet)
         }
         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 @@ static void pstore_timefunc(unsigned long dummy)
  */
 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 @@ 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, 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;
 }