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| author | Paul E. McKenney <paulmck@kernel.org> | 2022-04-14 15:56:35 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-07-22 02:41:56 +0200 |
| commit | dd04140531b5d38b77ad9ff7b18117654be5bf5c (patch) | |
| tree | 424f03517fcd26e3d5483b664501269aa997bb5f /kernel/rcu/tree.h | |
| parent | rcu: Switch polled grace-period APIs to ->gp_seq_polled (diff) | |
| download | linux-dd04140531b5d38b77ad9ff7b18117654be5bf5c.tar.xz linux-dd04140531b5d38b77ad9ff7b18117654be5bf5c.zip | |
rcu: Make polled grace-period API account for expedited grace periods
Currently, this code could splat:
oldstate = get_state_synchronize_rcu();
synchronize_rcu_expedited();
WARN_ON_ONCE(!poll_state_synchronize_rcu(oldstate));
This situation is counter-intuitive and user-unfriendly. After all, there
really was a perfectly valid full grace period right after the call to
get_state_synchronize_rcu(), so why shouldn't poll_state_synchronize_rcu()
know about it?
This commit therefore makes the polled grace-period API aware of expedited
grace periods in addition to the normal grace periods that it is already
aware of. With this change, the above code is guaranteed not to splat.
Please note that the above code can still splat due to counter wrap on the
one hand and situations involving partially overlapping normal/expedited
grace periods on the other. On 64-bit systems, the second is of course
much more likely than the first. It is possible to modify this approach
to prevent overlapping grace periods from causing splats, but only at
the expense of greatly increasing the probability of counter wrap, as
in within milliseconds on 32-bit systems and within minutes on 64-bit
systems.
This commit is in preparation for polled expedited grace periods.
Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/
Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing
Cc: Brian Foster <bfoster@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree.h')
| -rw-r--r-- | kernel/rcu/tree.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 9c853033f159..5634e76106c4 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -325,6 +325,7 @@ struct rcu_state { unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ unsigned long gp_seq_polled; /* GP seq for polled API. */ unsigned long gp_seq_polled_snap; /* ->gp_seq_polled at normal GP start. */ + unsigned long gp_seq_polled_exp_snap; /* ->gp_seq_polled at expedited GP start. */ /* End of fields guarded by root rcu_node's lock. */ |