Changelog
v2 -> v3
- Merge modifications of pstore part in 2/2 to 1/2.
- Rename pstore_is_non_blocking_path() to pstore_cannot_block_path().
v1 -> v2
- Erase a logic checking the number of online cpus.
- Create a patchset to fix deadlocking issue in both pstore filesystem and
efi_pstore driver.
- Introduce a function, is_non_blocking_path(), to check if pstore
is in panic and emergency-restart paths (PATCH 1/2)
- Avoid efi_pstore_driver is blocked in non-blocking paths
such as nmi, panic and emergency-restart paths (PATCH 2/2)
[Issue]
There are some paths in kernel which shouldn't be blocked,
like NMI, panic case after stopping cpus, emergency-restart.
On the other hand, current pstore avoids blocking in a NMI path
but it may be blocked in other paths.
Also, an efi_pstore driver may be blocked in all of those paths
because it simply takes a spin lock at writing time.
If they are blocked in those paths, the system will hang up and
it has a big impact for users.
Here is an example scenario which pstore is blocked in panic path.
- cpuA grabs psinfo->buf_lock
- cpuB panics and calls smp_send_stop
- smp_send_stop sends IRQ to cpuA
after 1 second, cpuB gives up on cpuA and sends an NMI instead
- cpuA is now in an NMI handler while still holding buf_lock.
And then, cpuB is deadlocked by taking efi_pstore->lock again.
This case may happen if a firmware has a bug and cpuA is stuck in it.
[Solution]
This patchset avoids that pstore and efi_pstore driver are blocked
in the non-blocking paths like NMI, panic, and emrgency-restart
by introducing a function checking if they are in those paths.
Please see each patch for detailed explanations.
Seiji Aguchi (2):
[PATCH v3 1/2] pstore: Avoid deadlock in panic and emergency-restart path
[PATCH v3 2/2] efi_pstore: Avoid deadlock in non-blocking paths
drivers/firmware/efivars.c | 11 ++++++++++-
fs/pstore/platform.c | 34 ++++++++++++++++++++++++++++------
include/linux/pstore.h | 6 ++++++
3 files changed, 44 insertions(+), 7 deletions(-)
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