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Date:   Fri, 11 Jan 2019 20:39:28 +0100 (CET)
From:   Jiri Kosina <jikos@kernel.org>
To:     hpa@zytor.com
cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Nadav Amit <namit@vmware.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [PATCH v3 0/6] Static calls
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On Fri, 11 Jan 2019, hpa@zytor.com wrote:

> I still don't see why can't simply spin in the #BP handler until the 
> patch is complete.

I think this brings us to the already discussed possible deadlock, when 
one CPU#0 is in the middle of text_poke_bp(), CPU#1 is spinning inside 
spin_lock_irq*(&lock) and CPU#2 hits the breakpont while holding that very 
'lock'.

Then we're stuck forever, because CPU#1 will never handle the pending 
sync_core() IPI (it's not NMI).

Or have I misunderstood what you meant?

-- 
Jiri Kosina
SUSE Labs