Hi,
Changelog-v2
============
- Standardize on seqcount_LOCKNAME_t as the canonical reference for
sequence counters with associated locks, instead of v1
seqcount_LOCKTYPE_t.
- Use unique prefix "seqprop_*" for all seqcount_t/seqcount_LOCKNAME_t
property accessors.
- Touch-up the lock-unlock rationale for more clarity. Enforce writer
non-preemitiblity using "__seq_enforce_writer_non_preemptibility()".
Cover letter (v1)
=================
https://lkml.kernel.org/r/[email protected]
Preemption must be disabled before entering a sequence counter write
side critical section. Otherwise the read side section can preempt the
write side section and spin for the entire scheduler tick. If that
reader belongs to a real-time scheduling class, it can spin forever and
the kernel will livelock.
Disabling preemption cannot be done for PREEMPT_RT though: it can lead
to higher latencies, and the write side sections will not be able to
acquire locks which become sleeping locks (e.g. spinlock_t).
To remain preemptible, while avoiding a possible livelock caused by the
reader preempting the writer, use a different technique: let the reader
detect if a seqcount_LOCKNAME_t writer is in progress. If that's the
case, acquire then release the associated LOCKNAME writer serialization
lock. This will allow any possibly-preempted writer to make progress
until the end of its writer serialization lock critical section.
Implement this lock-unlock technique for all seqcount_LOCKNAME_t with
an associated (PREEMPT_RT) sleeping lock, and for seqlock_t.
8<--------------
Ahmed S. Darwish (5):
seqlock: seqcount_LOCKNAME_t: Standardize naming convention
seqlock: Use unique prefix for seqcount_t property accessors
seqlock: seqcount_t: Implement all read APIs as statement expressions
seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support
seqlock: PREEMPT_RT: Do not starve seqlock_t writers
include/linux/seqlock.h | 281 ++++++++++++++++++++++++----------------
1 file changed, 167 insertions(+), 114 deletions(-)
base-commit: f75aef392f869018f78cfedf3c320a6b3fcfda6b
--
2.28.0
