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In-Reply-To: <20180426101902.22886-1-mpe@ellerman.id.au>
To: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@ozlabs.org
From: Michael Ellerman <patch-notifications@ellerman.id.au>
Cc: npiggin@gmail.com
Subject: Re: [v3] powerpc: Fix smp_send_stop NMI IPI handling
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Date: Thu, 26 Apr 2018 20:22:44 +1000 (AEST)
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On Thu, 2018-04-26 at 10:19:02 UTC, Michael Ellerman wrote:
> From: Nicholas Piggin <npiggin@gmail.com>
> 
> The NMI IPI handler for a receiving CPU increments nmi_ipi_busy_count
> over the handler function call, which causes later smp_send_nmi_ipi()
> callers to spin until the call is finished.
> 
> The stop_this_cpu() function never returns, so the busy count is never
> decremeted, which can cause the system to hang in some cases. For
> example panic() will call smp_send_stop() early on which calls
> stop_this_cpu() on other CPUs, then later in the reboot path,
> pnv_restart() will call smp_send_stop() again, which hangs.
> 
> Fix this by adding a special case to the stop_this_cpu() handler to
> decrement the busy count, because it will never return.
> 
> Now that the NMI/non-NMI versions of stop_this_cpu() are different,
> split them out into separate functions rather than doing #ifdef tricks
> to share the body between the two functions.
> 
> Fixes: 6bed3237624e3 ("powerpc: use NMI IPI for smp_send_stop")
> Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> [mpe: Split out the functions, tweak change log a bit]
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/ac61c1156623455c46701654abd8c9

cheers