Messages in this thread | | | Subject | Re: [patch V4 part 5 07/31] x86/entry: Provide idtentry_entry/exit_cond_rcu() | From | Alexandre Chartre <> | Date | Mon, 11 May 2020 15:53:17 +0200 |
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On 5/5/20 3:53 PM, Thomas Gleixner wrote: > The pagefault handler cannot use the regular idtentry_enter() because on > that invokes rcu_irq_enter() the pagefault was caused in the kernel.
I am struggling to understand this part of the sentence: "because on that invokes rcu_irq_enter() the pagefault was caused in the kernel."
Do you mean: "because that invokes rcu_irq_enter() if the pagefault was caused in the kernel." ?
alex.
> Not a > problem per se, but kernel side page faults can schedule which is not > possible without invoking rcu_irq_exit(). > > Adding rcu_irq_exit() and a matching rcu_irq_enter() into the actual > pagefault handling code is possible, but not pretty either. > > Provide idtentry_entry/exit_cond_rcu() which calls rcu_irq_enter() only > when RCU is not watching. While this is not a legit kernel #PF establishing > RCU before handling it avoids RCU side effects which might affect > debugability. > > The function is also useful for implementing lightweight scheduler IPI > entry handling later. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > arch/x86/entry/common.c | 119 ++++++++++++++++++++++++++++++++++------ > arch/x86/include/asm/idtentry.h | 3 + > 2 files changed, 106 insertions(+), 16 deletions(-)
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