This is the second attempt at fixing the behavior of igb_msix_other()
for PREEMPT_RT. The previous attempt [1] was reverted [2] following
concerns raised by Sebastian [3].
The initial approach proposed converting vfs_lock to a raw_spinlock,
a minor change intended to make it safe. However, it became evident
that igb_rcv_msg_from_vf() invokes kcalloc with GFP_ATOMIC,
which is unsafe in interrupt context on PREEMPT_RT systems.
To address this, the solution involves splitting igb_msg_task()
into two parts:
* One part invoked from the IRQ context.
* Another part called from the threaded interrupt handler.
To accommodate this, vfs_lock has been restructured into a double
lock: a spinlock_t and a raw_spinlock_t. In the revised design:
* igb_disable_sriov() locks both spinlocks.
* Each part of igb_msg_task() locks the appropriate spinlock for
its execution context.
It is worth noting that the double lock mechanism is only active under
PREEMPT_RT. For non-PREEMPT_RT builds, the additional raw_spinlock_t
field is ommited.
If the extra raw_spinlock_t field can be tolerated under
!PREEMPT_RT (even though it remains unused), we can eliminate the
need for #ifdefs and simplify the code structure.
I will be on vacation from December 7th to Christmas and will address
review comments upon my return.
If possible, I kindly request the Intel team to perform smoke tests
on both stock and realtime kernels to catch any potential issues with
this patch series.
Cheers,
Wander
[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/[email protected]/
[3] https://lore.kernel.org/all/[email protected]/
Wander Lairson Costa (4):
igb: narrow scope of vfs_lock in SR-IOV cleanup
igb: introduce raw vfs_lock to igb_adapter
igb: split igb_msg_task()
igb: fix igb_msix_other() handling for PREEMPT_RT
drivers/net/ethernet/intel/igb/igb.h | 4 +
drivers/net/ethernet/intel/igb/igb_main.c | 160 +++++++++++++++++++---
2 files changed, 148 insertions(+), 16 deletions(-)
--
2.47.0
