[PATCH v6 -next 0/2] make efivars/efi_pstore interrupt-safe

[Seiji Aguchi]

Changelog
v5 -> v6
   - Rebase to a latest linux-next tree.
   - Modify a comment from "efivar_update_sysfs_entry" to 
     "efivar_update_sysfs_entries" in include/linux/efi.h (Patch 2/2)

v4 -> v5
   - Rebase from a linus tree to a linux-next tree to avoid getting
     a conflict when this patchset is merged to a linux-next tree.
   - Merge previous patches 2/3 and 3/3 into 2/2 because they fix
     a same problem.
   - Modify to fit a latest upstream kernel as follows.
    - Change spinlock operations of efivarfs which has been 
      introduced recently.(Patch 1/2)
    - Remove delete_all_stale_sysfs_entries() from update_sysfs_entries()
      because a currnet efi_pstore doesn't erase existing entries
      in a write callback and sysfs entries don't become stale. 
      (Patch 2/2)

v3 -> v4
  - Patch 2/3
    Move cancel_work_sync() above an efi_enabled test in efivars_exit().

v2 -> v3
  - Patch 1/3
    Replace spin_lock_irqsave/spin_unlock_irqrestore with spin_lock_irq/spin_unlock_irq in efivars_unregister(),
    efivar_create(), efivar_store_raw() and efivar_delete() which are called in a process context. 

 - Patch 2/3
    Change a name of delete_sysfs_entry() to delete_all_stale_sysfs_entries().
    Also, don't release an efivar->lock while searching efivar->list in delete_all_stale_sysfs_entries().

 - Patch 3/3
    Remove a logic in efi_pstore_erase() which freshly created in patch v2.

v1 -> v2
 - 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 efivars
 including efivarfs and efi_pstore.

(1)There is a scenario which efi_pstore fails to log messages 
   in a panic case.

   - CPUA holds an efi_var->lock in either efivarfs parts 
     or efi_pstore with interrupt enabled.
   - CPUB panics and sends IPI to CPUA in smp_send_stop().
   - CPUA stops with holding the lock.
   - CPUB kicks efi_pstore_write() via kmsg_dump(KSMG_DUMP_PANIC)
     but it returns without logging messages.

(2)Also, efi_pstore creates sysfs entries, which enable users to access to 
   NVRAM, in a write callback.
   If a kernel panic happens in an interrupt contexts, pstore may fail
   because it could sleep due to dynamic memory allocations during creating 
   sysfs entries.
   An actual failure due to the create_sysfs_entry() has been reported.
   http://comments.gmane.org/gmane.linux.kernel.efi/406

To resolve problems above, this patchset makes efivars/efi_pstore
interrupt-safe.

[Patch Description]
  Please see detailed explanations in each patch.

Seiji Aguchi (2):
  efivars: Disable external interrupt while holding efivars->lock
  efi_pstore: Introducing workqueue updating sysfs entries

 drivers/firmware/efivars.c |  171 ++++++++++++++++++++++++++++++++------------
 include/linux/efi.h        |    3 +-
 2 files changed, 126 insertions(+), 48 deletions(-)

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