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, 1 insertions, 1 deletions

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index eb80b549ed8d..be8bcb035e2a 100644
--- 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);
         }