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srcu: Bit manipulation changes for additional reader flavor

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Currently, there are only two flavors of readers, normal and NMI-safe.
Very straightforward state updates suffice to check for erroneous
mixing of reader flavors on a given srcu_struct structure.  This commit
upgrades the checking in preparation for the addition of light-weight
(as in memory-barrier-free) readers.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Paul E. McKenney 2024-10-15 09:11:01 -07:00 committed by Frederic Weisbecker
parent 365f34483b
commit c2f9467c77
1 changed files with 4 additions and 3 deletions
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7
kernel/rcu/srcutree.c
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@ -462,7 +462,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
if (IS_ENABLED(CONFIG_PROVE_RCU))
mask = mask | READ_ONCE(cpuc->srcu_reader_flavor);
}
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)),
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
"Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
return sum;
}
@ -712,8 +712,9 @@ void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
sdp = raw_cpu_ptr(ssp->sda);
old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
if (!old_reader_flavor_mask) {
WRITE_ONCE(sdp->srcu_reader_flavor, reader_flavor_mask);
return;
old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask);
if (!old_reader_flavor_mask)
return;
}
WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask);
}