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/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
index 2ca59dc..5e820ea 100644 (file)
--- a/drivers/acpi/apei/erst.c
+++ b/drivers/acpi/apei/erst.c
@@ -1165,7 +1165,7 @@ 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/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index eb80b54..be8bcb0 100644 (file)
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -978,7 +978,7 @@ int register_efivars(struct efivars *efivars,
        if (efivars->efi_pstore_info.buf) {
                efivars->efi_pstore_info.bufsize = 1024;
                efivars->efi_pstore_info.data = efivars;
-               mutex_init(&efivars->efi_pstore_info.buf_mutex);
+               spin_lock_init(&efivars->efi_pstore_info.buf_lock);
                pstore_register(&efivars->efi_pstore_info);
        }
 

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index ca60ebc..0472924 100644 (file)
--- 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;
 }

diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index cc03bbf..b91440e 100644 (file)
--- 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);