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rcu: Use WRITE_ONCE() for ->rcu_need_heavy_qs

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Currently raw_cpu_write() is used to clear the ->rcu_need_heavy_qs
field of the per-CPU rcu_data structure.  However, on x86 this is a
normal assignment, which does not play well with concurrent accesses.
This commit therefore upgrades the uses of raw_cpu_write() to its
concurrency-safe counterpart WRITE_ONCE() of an rdp pointer obtained
from this_cpu_ptr(&rcu_data).

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2026-07-16 13:05:00 -07:00
parent d2282f9bc7
commit a050e671d3
1 changed files with 2 additions and 1 deletions
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3
kernel/rcu/tree.c
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@ -357,9 +357,10 @@ bool rcu_watching_zero_in_eqs(int cpu, int *vp)
*/
notrace void rcu_momentary_eqs(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
int seq;
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
seq = ct_state_inc(2 * CT_RCU_WATCHING);
/* It is illegal to call this from idle state. */
WARN_ON_ONCE(!(seq & CT_RCU_WATCHING));