From 414c12385d4741e35d88670c6cc2f40a77809734 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 13 Apr 2022 15:17:25 -0700 Subject: rcu: Provide a get_completed_synchronize_rcu() function It is currently up to the caller to handle stale return values from get_state_synchronize_rcu(). If poll_state_synchronize_rcu() returned true once, a grace period has elapsed, regardless of the fact that counter wrap might cause some future poll_state_synchronize_rcu() invocation to return false. For example, the caller might store a separate flag that indicates whether some previous call to poll_state_synchronize_rcu() determined that the relevant grace period had already ended. This approach works, but it requires extra storage and is easy to get wrong. This commit therefore introduces a get_completed_synchronize_rcu() that returns a cookie that causes poll_state_synchronize_rcu() to always return true. This already-completed cookie can be stored in place of the cookie that previously caused poll_state_synchronize_rcu() to return true. It can also be used to flag a given structure as not having been exposed to readers, and thus not requiring a grace period to elapse. This commit is in preparation for polled expedited grace periods. Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/ Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing Cc: Brian Foster Cc: Dave Chinner Cc: Al Viro Cc: Ian Kent Signed-off-by: Paul E. McKenney --- kernel/rcu/tiny.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu/tiny.c') diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 340b3f8b090d..dbee6bea6726 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -58,7 +58,7 @@ void rcu_qs(void) rcu_ctrlblk.donetail = rcu_ctrlblk.curtail; raise_softirq_irqoff(RCU_SOFTIRQ); } - WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 1); + WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); local_irq_restore(flags); } @@ -213,7 +213,7 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); */ bool poll_state_synchronize_rcu(unsigned long oldstate) { - return READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate; + return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate; } EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); -- cgit v1.2.3-70-g09d2 From 800d6acf40e5ce676b53a1259fb4e93e56279367 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Fri, 27 May 2022 17:07:45 +0200 Subject: rcu: tiny: Record kvfree_call_rcu() call stack for KASAN When running KASAN with Tiny RCU (e.g. under ARCH=um, where a working KASAN patch is now available), we don't get any information on the original kfree_rcu() (or similar) caller when a problem is reported, as Tiny RCU doesn't record this. Add the recording, which required pulling kvfree_call_rcu() out of line for the KASAN case since the recording function (kasan_record_aux_stack_noalloc) is neither exported, nor can we include kasan.h into rcutiny.h. without KASAN, the patch has no size impact (ARCH=um kernel): text data bss dec hex filename 6151515 4423154 33148520 43723189 29b29b5 linux 6151515 4423154 33148520 43723189 29b29b5 linux + patch with KASAN, the impact on my build was minimal: text data bss dec hex filename 13915539 7388050 33282304 54585893 340ea25 linux 13911266 7392114 33282304 54585684 340e954 linux + patch -4273 +4064 +-0 -209 Acked-by: Dmitry Vyukov Signed-off-by: Johannes Berg Signed-off-by: Paul E. McKenney --- include/linux/rcutiny.h | 11 ++++++++++- kernel/rcu/tiny.c | 14 ++++++++++++++ 2 files changed, 24 insertions(+), 1 deletion(-) (limited to 'kernel/rcu/tiny.c') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 5fed476f977f..d84e13f2c384 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -38,7 +38,7 @@ static inline void synchronize_rcu_expedited(void) */ extern void kvfree(const void *addr); -static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) +static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) { if (head) { call_rcu(head, func); @@ -51,6 +51,15 @@ static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) kvfree((void *) func); } +#ifdef CONFIG_KASAN_GENERIC +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func); +#else +static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) +{ + __kvfree_call_rcu(head, func); +} +#endif + void rcu_qs(void); static inline void rcu_softirq_qs(void) diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 340b3f8b090d..58ff3721d975 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -217,6 +217,20 @@ bool poll_state_synchronize_rcu(unsigned long oldstate) } EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); +#ifdef CONFIG_KASAN_GENERIC +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) +{ + if (head) { + void *ptr = (void *) head - (unsigned long) func; + + kasan_record_aux_stack_noalloc(ptr); + } + + __kvfree_call_rcu(head, func); +} +EXPORT_SYMBOL_GPL(kvfree_call_rcu); +#endif + void __init rcu_init(void) { open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); -- cgit v1.2.3-70-g09d2 From 7f4535366f8f77b3ddbc79d4ba82df966c5c2aab Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 14 Apr 2022 11:49:58 -0700 Subject: rcu: Make Tiny RCU grace periods visible to polled APIs This commit makes the Tiny RCU implementation of synchronize_rcu() increment the rcu_ctrlblk.gp_seq counter, thus making both synchronize_rcu() and synchronize_rcu_expedited() visible to get_state_synchronize_rcu() and friends. Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/ Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing Cc: Brian Foster Cc: Dave Chinner Cc: Al Viro Cc: Ian Kent Signed-off-by: Paul E. McKenney --- kernel/rcu/tiny.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'kernel/rcu/tiny.c') diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index dbee6bea6726..60071817d939 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -139,8 +139,10 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused /* * Wait for a grace period to elapse. But it is illegal to invoke * synchronize_rcu() from within an RCU read-side critical section. - * Therefore, any legal call to synchronize_rcu() is a quiescent - * state, and so on a UP system, synchronize_rcu() need do nothing. + * Therefore, any legal call to synchronize_rcu() is a quiescent state, + * and so on a UP system, synchronize_rcu() need do nothing, other than + * let the polled APIs know that another grace period elapsed. + * * (But Lai Jiangshan points out the benefits of doing might_sleep() * to reduce latency.) * @@ -152,6 +154,7 @@ void synchronize_rcu(void) lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); + WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); } EXPORT_SYMBOL_GPL(synchronize_rcu); -- cgit v1.2.3-70-g09d2