Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 02/20] context_tracking: Add a note about noinstr VS unsafe context tracking functions | Date | Tue, 28 Jun 2022 15:16:01 +0200 |
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Some context tracking functions enter or exit into/from RCU idle mode while using trace-able and lockdep-aware IRQs (un-)masking. As a result those functions can't get tagged as noinstr. This is unlikely to be fixed since these are obsolete APIs. Drop a note about this matter.
[ paulmck: Apply Peter Zijlstra feedback. ]
Reported-by: Peter Zijlstra <peterz@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Uladzislau Rezki <uladzislau.rezki@sony.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Nicolas Saenz Julienne <nsaenz@kernel.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com> Cc: Yu Liao <liaoyu15@huawei.com> Cc: Phil Auld <pauld@redhat.com> Cc: Paul Gortmaker<paul.gortmaker@windriver.com> Cc: Alex Belits <abelits@marvell.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> --- kernel/context_tracking.c | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+)
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 36a98c48aedc..3082332f6476 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -103,6 +103,15 @@ void noinstr __context_tracking_enter(enum ctx_state state) } EXPORT_SYMBOL_GPL(__context_tracking_enter); +/* + * OBSOLETE: + * This function should be noinstr but the below local_irq_restore() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call __context_tracking_enter() through user_enter_irqoff() + * or context_tracking_guest_enter(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ void context_tracking_enter(enum ctx_state state) { unsigned long flags; @@ -125,6 +134,14 @@ void context_tracking_enter(enum ctx_state state) NOKPROBE_SYMBOL(context_tracking_enter); EXPORT_SYMBOL_GPL(context_tracking_enter); +/* + * OBSOLETE: + * This function should be noinstr but it unsafely calls local_irq_restore(), + * involving illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call user_enter_irqoff(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ void context_tracking_user_enter(void) { user_enter(); @@ -168,6 +185,15 @@ void noinstr __context_tracking_exit(enum ctx_state state) } EXPORT_SYMBOL_GPL(__context_tracking_exit); +/* + * OBSOLETE: + * This function should be noinstr but the below local_irq_save() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call __context_tracking_exit() through user_exit_irqoff() + * or context_tracking_guest_exit(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ void context_tracking_exit(enum ctx_state state) { unsigned long flags; @@ -182,6 +208,14 @@ void context_tracking_exit(enum ctx_state state) NOKPROBE_SYMBOL(context_tracking_exit); EXPORT_SYMBOL_GPL(context_tracking_exit); +/* + * OBSOLETE: + * This function should be noinstr but it unsafely calls local_irq_save(), + * involving illegal RCU uses through tracing and lockdep. This is unlikely + * to be fixed as this function is obsolete. The preferred way is to call + * user_exit_irqoff(). It should be the arch entry code responsibility to + * call into context tracking with IRQs disabled. + */ void context_tracking_user_exit(void) { user_exit(); -- 2.25.1
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