[PATCH 0/5] turn signal_struct.stats_lock into seqcount_rwlock_t

Oleg Nesterov
2023-09-13T15:51:09Z

Hello,

RFC, not for inclusion yet. Please review, at least the intent.

In particular, can you look at the changelog from the last patch?
Am I right that currently thread_group_cputime() is not RT friendly?

During the (ongoing) s/while_each_thread/for_each_thread/ conversion
I noticed that some of these users can use signal->stats_lock instead
of lock_task_sighand(). And if we change them, we can try to avoid
stats_lock under siglock in wait_task_zombie() at least.

However, signal->stats_lock is seqlock_t but I think seqcount_rwlock_t
make more sense. So let me try to turn it into seqcount_rwlock_t first.

OTOH... I am not sure I understand the value of signal->stats_lock.
I mean, do we have any numbers which prove that seqlock_t is really
"better" than the plain rwlock_t ?

So far only compile tested, and I need to re-read these changes with
a clear head. In any case, it is not that I myself like this series
very much, and most probably I did something wrong...

Oleg.
---
include/linux/sched/signal.h | 4 +-
include/linux/seqlock.h | 105 +++++++++++++++++++++++++++++++++++--------
kernel/exit.c | 12 +++--
kernel/fork.c | 3 +-
kernel/sched/cputime.c | 10 +++--
5 files changed, 106 insertions(+), 28 deletions(-)