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

From: Seiji Aguchi
Date: Mon Feb 11 2013 - 12:59:14 EST

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.

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.

To resolve problems above, this patchset makes efivars/efi_pstore

[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(-)

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/