srcu: Unconditionally record srcu_read_lock_lite() in ->srcu_reader_flavor

Currently, srcu_read_lock_lite() uses the SRCU_READ_FLAVOR_LITE bit in
->srcu_reader_flavor to communicate to the grace-period processing in
srcu_readers_active_idx_check() that the smp_mb() must be replaced by a
synchronize_rcu().  Unfortunately, ->srcu_reader_flavor is not updated
unless the kernel is built with CONFIG_PROVE_RCU=y.  Therefore in all
kernels built with CONFIG_PROVE_RCU=n, srcu_readers_active_idx_check()
incorrectly uses smp_mb() instead of synchronize_rcu() for srcu_struct
structures whose readers use srcu_read_lock_lite().

This commit therefore causes Tree SRCU srcu_read_lock_lite()
to unconditionally update ->srcu_reader_flavor so that
srcu_readers_active_idx_check() can make the correct choice.

Reported-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/
Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

1 files changed, 1 insertions, 7 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 56f83237de4d..08339eb8a01c 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -183,12 +183,6 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
-void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
-#else
-#define srcu_check_read_flavor(ssp, read_flavor) do { } while (0)
-#endif
-
 
 /**
  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
@@ -277,7 +271,7 @@ static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;
 
-	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
+	srcu_check_read_flavor_lite(ssp);
 	retval = __srcu_read_lock_lite(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;