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: NDon Zickus <dzickus@redhat.com>
Acked-by: NMatthew Garrett <mjg@redhat.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

We'll never have a negative part, so just make this an unsigned int.
Signed-off-by: NMatthew Garrett <mjg@redhat.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

EFI only provides small amounts of individual storage, and conventionally
puts metadata in the storage variable name. Rather than add a metadata
header to the (already limited) variable storage, it's easier for us to
modify pstore to pass all the information we need to construct a unique
variable name to the appropriate functions.
Signed-off-by: NMatthew Garrett <mjg@redhat.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

Some pstore implementations may not have a static context, so extend the
API to pass the pstore_info struct to all calls and allow for a context
pointer.
Signed-off-by: NMatthew Garrett <mjg@redhat.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

Currently after mount/remount operation on pstore filesystem,
the content on pstore will be lost. It is because current ERST
implementation doesn't support multi-user usage, which moves
internal pointer to the end after accessing it. Adding
multi-user support for pstore usage.
Signed-off-by: NChen Gong <gong.chen@linux.intel.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

the return type of function _read_ in pstore is size_t,
but in the callback function of _read_, the logic doesn't
consider it too much, which means if negative value (assuming
error here) is returned, it will be converted to positive because
of type casting. ssize_t is enough for this function.
Signed-off-by: NChen Gong <gong.chen@linux.intel.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

Some platforms have a small amount of non-volatile storage that
can be used to store information useful to diagnose the cause of
a system crash.  This is the generic part of a file system interface
that presents information from the crash as a series of files in
/dev/pstore.  Once the information has been seen, the underlying
storage is freed by deleting the files.
Signed-off-by: NTony Luck <tony.luck@intel.com>