Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 04/21] context_tracking: Add a note about noinstr VS unsafe context tracking functions | Date | Tue, 3 May 2022 12:00:34 +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. This could be easily solved with using raw versions of local_irq_*() but we would then lose some precious debugging informations.
Another possible way to solve this may consist in using rude RCU-tasks in lockdep and irqsoff tracing.
In any case and until this get solved, those functions can't get tagged as noinstr even though they should.
Reported-by: Peter Zijlstra <peterz@infradead.org> Cc: Paul E. McKenney <paulmck@kernel.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> --- kernel/context_tracking.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 36a98c48aedc..1f44b0461d14 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -103,6 +103,11 @@ void noinstr __context_tracking_enter(enum ctx_state state) } EXPORT_SYMBOL_GPL(__context_tracking_enter); +/* + * FIXME: This function should be noinstr but the below local_irq_restore() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. This + * must be fixed first. + */ void context_tracking_enter(enum ctx_state state) { unsigned long flags; @@ -125,6 +130,10 @@ void context_tracking_enter(enum ctx_state state) NOKPROBE_SYMBOL(context_tracking_enter); EXPORT_SYMBOL_GPL(context_tracking_enter); +/* + * FIXME: This function should be noinstr but it unsafely calls local_irq_restore(), + * involving illegal RCU uses through tracing and lockdep. This must be fixed first. + */ void context_tracking_user_enter(void) { user_enter(); @@ -168,6 +177,11 @@ void noinstr __context_tracking_exit(enum ctx_state state) } EXPORT_SYMBOL_GPL(__context_tracking_exit); +/* + * FIXME: This function should be noinstr but the below local_irq_save() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. This + * must be fixed first. + */ void context_tracking_exit(enum ctx_state state) { unsigned long flags; @@ -182,6 +196,10 @@ void context_tracking_exit(enum ctx_state state) NOKPROBE_SYMBOL(context_tracking_exit); EXPORT_SYMBOL_GPL(context_tracking_exit); +/* + * FIXME: This function should be noinstr but it unsafely calls local_irq_save(), + * involving illegal RCU uses through tracing and lockdep. This must be fixed first. + */ void context_tracking_user_exit(void) { user_exit(); -- 2.25.1
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