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context_tracking: Add a note about noinstr VS unsafe context tracking functions

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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>
This commit is contained in:
Frederic Weisbecker 2022-06-08 16:40:19 +02:00 committed by Paul E. McKenney
parent 5f8a62af52
commit f67671baad
1 changed files with 34 additions and 0 deletions
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34
kernel/context_tracking.c
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@ -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* This is unlikely to be fixed as this function is obsolete.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();