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Groups > linux.kernel > #1738256
| From | Linus Torvalds <torvalds@linux-foundation.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers |
| Date | 2017-09-24 21:50 +0200 |
| Message-ID | <utl4B-4jB-7@gated-at.bofh.it> (permalink) |
| References | <usZGN-7Ze-7@gated-at.bofh.it> <usZGN-7Ze-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Sat, Sep 23, 2017 at 1:56 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> +
> + /* Page faults can happen in NMI handlers, so check... */
> + if (READ_ONCE(rdtp->dynticks_nmi_nesting))
> + return;
> +
What is the reason for the READ_ONCE() here (and in the other case)?
It doesn't seem to have any actual reason. It's a "stable" per-cpu
value in that even if an NMI were to happen, it gets incremented and
then decremented, so there is nothing really volatile about it
anywhere that I can see.
So the READ_ONCE() seems to be just pure confusion.
What am I missing?
Linus
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[PATCH 1/4] rcu: Allow for page faults in NMI handlers Steven Rostedt <rostedt@goodmis.org> - 2017-09-23 23:00 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers Linus Torvalds <torvalds@linux-foundation.org> - 2017-09-24 21:50 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-25 02:10 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers Linus Torvalds <torvalds@linux-foundation.org> - 2017-09-25 02:20 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-25 02:30 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-25 02:40 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers Steven Rostedt <rostedt@goodmis.org> - 2017-09-25 06:50 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-25 07:00 +0200
Re: [PATCH 1/4] rcu: Allow for page faults in NMI handlers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-26 05:20 +0200
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