From f87d28673b71b35b248231a2086f9404afbb7f28 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Sat, 25 Feb 2023 16:01:36 -0800 Subject: [PATCH 1/2] entry: Fix noinstr warning in __enter_from_user_mode() __enter_from_user_mode() is triggering noinstr warnings with CONFIG_DEBUG_PREEMPT due to its call of preempt_count_add() via ct_state(). The preemption disable isn't needed as interrupts are already disabled. And the context_tracking_enabled() check in ct_state() also isn't needed as that's already being done by the CT_WARN_ON(). Just use __ct_state() instead. Fixes the following warnings: vmlinux.o: warning: objtool: enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0xf9: call to preempt_count_add() leaves .noinstr.text section vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0xc7: call to preempt_count_add() leaves .noinstr.text section vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section Fixes: 171476775d32 ("context_tracking: Convert state to atomic_t") Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/d8955fa6d68dc955dda19baf13ae014ae27926f5.1677369694.git.jpoimboe@kernel.org --- include/linux/context_tracking.h | 1 + include/linux/context_tracking_state.h | 2 ++ kernel/entry/common.c | 2 +- 3 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index d4afa8508a80..3a7909ed5498 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -96,6 +96,7 @@ static inline void user_exit_irqoff(void) { } static inline int exception_enter(void) { return 0; } static inline void exception_exit(enum ctx_state prev_ctx) { } static inline int ct_state(void) { return -1; } +static inline int __ct_state(void) { return -1; } static __always_inline bool context_tracking_guest_enter(void) { return false; } static inline void context_tracking_guest_exit(void) { } #define CT_WARN_ON(cond) do { } while (0) diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index 4a4d56f77180..fdd537ea513f 100644 --- a/include/linux/context_tracking_state.h +++ b/include/linux/context_tracking_state.h @@ -46,7 +46,9 @@ struct context_tracking { #ifdef CONFIG_CONTEXT_TRACKING DECLARE_PER_CPU(struct context_tracking, context_tracking); +#endif +#ifdef CONFIG_CONTEXT_TRACKING_USER static __always_inline int __ct_state(void) { return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK; diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 846add8394c4..1314894d2efa 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -21,7 +21,7 @@ static __always_inline void __enter_from_user_mode(struct pt_regs *regs) arch_enter_from_user_mode(regs); lockdep_hardirqs_off(CALLER_ADDR0); - CT_WARN_ON(ct_state() != CONTEXT_USER); + CT_WARN_ON(__ct_state() != CONTEXT_USER); user_exit_irqoff(); instrumentation_begin(); From b416514054810cf2d2cc348ae477cea619b64da7 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 15 Mar 2023 19:43:43 +0000 Subject: [PATCH 2/2] entry/rcu: Check TIF_RESCHED _after_ delayed RCU wake-up RCU sometimes needs to perform a delayed wake up for specific kthreads handling offloaded callbacks (RCU_NOCB). These wakeups are performed by timers and upon entry to idle (also to guest and to user on nohz_full). However the delayed wake-up on kernel exit is actually performed after the thread flags are fetched towards the fast path check for work to do on exit to user. As a result, and if there is no other pending work to do upon that kernel exit, the current task will resume to userspace with TIF_RESCHED set and the pending wake up ignored. Fix this with fetching the thread flags _after_ the delayed RCU-nocb kthread wake-up. Fixes: 47b8ff194c1f ("entry: Explicitly flush pending rcuog wakeup before last rescheduling point") Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230315194349.10798-3-joel@joelfernandes.org --- kernel/entry/common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 1314894d2efa..be61332c66b5 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -192,13 +192,14 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, static void exit_to_user_mode_prepare(struct pt_regs *regs) { - unsigned long ti_work = read_thread_flags(); + unsigned long ti_work; lockdep_assert_irqs_disabled(); /* Flush pending rcuog wakeup before the last need_resched() check */ tick_nohz_user_enter_prepare(); + ti_work = read_thread_flags(); if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work);