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.upadh...@amd.com> Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c5...@amd.com/ Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()" Signed-off-by: Paul E. McKenney <paul...@kernel.org> Cc: Frederic Weisbecker <frede...@kernel.org> --- include/linux/srcu.h | 8 +------- include/linux/srcutiny.h | 3 +++ include/linux/srcutree.h | 21 +++++++++++++++++++++ kernel/rcu/srcutree.c | 6 ++---- 4 files changed, 27 insertions(+), 11 deletions(-) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index fff6265818d4f..abaddd7e6ddf7 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 @@ -278,7 +272,7 @@ 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; diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index 4d96bbdb45f08..1321da803274d 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -81,6 +81,9 @@ static inline void srcu_barrier(struct srcu_struct *ssp) synchronize_srcu(ssp); } +#define srcu_check_read_flavor(ssp, read_flavor) do { } while (0) +#define srcu_check_read_flavor_lite(ssp) do { } while (0) + /* Defined here to avoid size increase for non-torture kernels. */ static inline void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 778eb61542e18..490aeecc6bb47 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -248,4 +248,25 @@ static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite()."); } +void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); + +// Record _lite() usage even for CONFIG_PROVE_RCU=n kernels. +static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp) +{ + struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); + + if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE)) + return; + + // Note that the cmpxchg() in srcu_check_read_flavor() is fully ordered. + __srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE); +} + +// Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels. +static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) +{ + if (IS_ENABLED(CONFIG_PROVE_RCU)) + __srcu_check_read_flavor(ssp, read_flavor); +} + #endif diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 5991381b44383..ee3cbb8308664 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -711,11 +711,10 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(cleanup_srcu_struct); -#ifdef CONFIG_PROVE_RCU /* * Check for consistent reader flavor. */ -void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) +void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) { int old_read_flavor; struct srcu_data *sdp; @@ -733,8 +732,7 @@ void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) } WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor); } -EXPORT_SYMBOL_GPL(srcu_check_read_flavor); -#endif /* CONFIG_PROVE_RCU */ +EXPORT_SYMBOL_GPL(__srcu_check_read_flavor); /* * Counts the new reader in the appropriate per-CPU element of the -- 2.40.1
