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rcu: Eliminate lockless accesses to rcu_sync->gp_count

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The rcu_sync structure's ->gp_count field is always accessed under the
protection of that same structure's ->rss_lock field, with the exception
of a pair of WARN_ON_ONCE() calls just prior to acquiring that lock in
functions rcu_sync_exit() and rcu_sync_dtor().  These lockless accesses
are unnecessary and impair KCSAN's ability to catch bugs that might be
inserted via other lockless accesses.

This commit therefore moves those WARN_ON_ONCE() calls under the lock.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Oleg Nesterov 2024-05-12 08:02:07 -07:00 committed by Paul E. McKenney
parent 7f09e70f9e
commit 6f4cec22c3
1 changed files with 4 additions and 8 deletions
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12
kernel/rcu/sync.c
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@ -122,7 +122,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
* we are called at early boot time but this shouldn't happen. * we are called at early boot time but this shouldn't happen.
*/ */
} }
WRITE_ONCE(rsp->gp_count, rsp->gp_count + 1); rsp->gp_count++;
spin_unlock_irq(&rsp->rss_lock); spin_unlock_irq(&rsp->rss_lock);
if (gp_state == GP_IDLE) { if (gp_state == GP_IDLE) {
@ -151,15 +151,11 @@ void rcu_sync_enter(struct rcu_sync *rsp)
*/ */
void rcu_sync_exit(struct rcu_sync *rsp) void rcu_sync_exit(struct rcu_sync *rsp)
{ {
int gpc;
WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_IDLE); WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_IDLE);
WARN_ON_ONCE(READ_ONCE(rsp->gp_count) == 0);
spin_lock_irq(&rsp->rss_lock); spin_lock_irq(&rsp->rss_lock);
gpc = rsp->gp_count - 1; WARN_ON_ONCE(rsp->gp_count == 0);
WRITE_ONCE(rsp->gp_count, gpc); if (!--rsp->gp_count) {
if (!gpc) {
if (rsp->gp_state == GP_PASSED) { if (rsp->gp_state == GP_PASSED) {
WRITE_ONCE(rsp->gp_state, GP_EXIT); WRITE_ONCE(rsp->gp_state, GP_EXIT);
rcu_sync_call(rsp); rcu_sync_call(rsp);
@ -178,10 +174,10 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
{ {
int gp_state; int gp_state;
WARN_ON_ONCE(READ_ONCE(rsp->gp_count));
WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_PASSED); WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_PASSED);
spin_lock_irq(&rsp->rss_lock); spin_lock_irq(&rsp->rss_lock);
WARN_ON_ONCE(rsp->gp_count);
if (rsp->gp_state == GP_REPLAY) if (rsp->gp_state == GP_REPLAY)
WRITE_ONCE(rsp->gp_state, GP_EXIT); WRITE_ONCE(rsp->gp_state, GP_EXIT);
gp_state = rsp->gp_state; gp_state = rsp->gp_state;