[Dle-develop] [RFC][PATCH v2 0/3] make efivars/efi_pstore interrupt-safe

[Seiji A. <sei...@hd...>]

Changelog
 - Patch 1/3
    Add spin_lock_irq/spin_unlock_irq to open/close callbacks of efi_pstore 
    instead of moving spin_locks to a read callback.    

 - Patch 2/3
    Replace a periodical timer with schedule_work().

 - Patch 3/3
    freshly create to kick a workqueue in oops case only.

[Problem]
 There are following problems related to an interrupt context in efivar/efi_pstore.

 Currently, efivars enables interrupt while taking efivars->lock.
 So, there is a risk to be deadlocking in a write callback of efi_pstore if kernel panics 
 in interrupt context while taking efi_lock.

 Also, efi_pstore creates sysfs entries ,which enable users to access to NVRAM, in a write callback.
 If a kernel panic happens in interrupt contexts, pstore may fail because it could sleep due to dynamic 
 memory allocations during creating sysfs entries.

To resolve the problems above, a goal of this patchset is making efivars/efi_pstore interrupt-safe.

[Patch Description]
 Patch 1/3 efivars: Disable external interrupt while holding efivars->lock
   This patch replaces spin_lock/spin_unlock with spin_lock_irqsave/spin_lock_irqrestore to make efivars interrupt safe

 Patch 2/3 efi_pstore: Introducing workqueue updating sysfs entries
   This patch removes sysfs operations from write callback by introducing a workqueue updating sysfs entries

 Patch 3/3 efi_pstore: Skip scheduling a workqueue in cases other than oops
   This patch restricts a schedule of a workqueue in just oops case which is truly needed for users.
   Also, a logic of erase callback is freshly created instead of sharing with a write callback so that
   its sysfs update operation works correctly.

 drivers/firmware/efivars.c |  209 +++++++++++++++++++++++++++++++++++++-------
 include/linux/efi.h        |    3 +-
 2 files changed, 179 insertions(+), 33 deletions(-)