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| author | David Woodhouse <dwmw@amazon.co.uk> | 2021-02-16 15:04:34 +0000 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-02-08 10:11:41 -0800 |
| commit | 82980b1622d97017053c6792382469d7dc26a486 (patch) | |
| tree | 86c9c34f1c04754f375294a3b1f3f5dc3426ad02 /kernel/rcu/tree.h | |
| parent | da123016ca8cb5697366c0b2dd55059b976e67e4 (diff) | |
| download | linux-stable-82980b1622d97017053c6792382469d7dc26a486.tar.gz linux-stable-82980b1622d97017053c6792382469d7dc26a486.tar.bz2 linux-stable-82980b1622d97017053c6792382469d7dc26a486.zip | |
rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock for exclusion
If we allow architectures to bring APs online in parallel, then we end
up requiring rcu_cpu_starting() to be reentrant. But currently, the
manipulation of rnp->ofl_seq is not thread-safe.
However, rnp->ofl_seq is also fairly much pointless anyway since both
rcu_cpu_starting() and rcu_report_dead() hold rcu_state.ofl_lock for
fairly much the whole time that rnp->ofl_seq is set to an odd number
to indicate that an operation is in progress.
So drop rnp->ofl_seq completely, and use only rcu_state.ofl_lock.
This has a couple of minor complexities: lockdep will complain when we
take rcu_state.ofl_lock, and currently accepts the 'excuse' of having
an odd value in rnp->ofl_seq. So switch it to an arch_spinlock_t to
avoid that false positive complaint. Since we're killing rnp->ofl_seq
of course that 'excuse' has to be changed too, so make it check for
arch_spin_is_locked(rcu_state.ofl_lock).
There's no arch_spin_lock_irqsave() so we have to manually save and
restore local interrupts around the locking.
At Paul's request based on Neeraj's analysis, make rcu_gp_init not just
wait but *exclude* any CPU online/offline activity, which was fairly
much true already by virtue of it holding rcu_state.ofl_lock.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree.h')
| -rw-r--r-- | kernel/rcu/tree.h | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 486fc901bd08..4b4bcef8a974 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -56,8 +56,6 @@ struct rcu_node { /* Initialized from ->qsmaskinitnext at the */ /* beginning of each grace period. */ unsigned long qsmaskinitnext; - unsigned long ofl_seq; /* CPU-hotplug operation sequence count. */ - /* Online CPUs for next grace period. */ unsigned long expmask; /* CPUs or groups that need to check in */ /* to allow the current expedited GP */ /* to complete. */ @@ -355,7 +353,7 @@ struct rcu_state { const char *name; /* Name of structure. */ char abbr; /* Abbreviated name. */ - raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; + arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; /* Synchronize offline with */ /* GP pre-initialization. */ }; |