Re: [PATCH] Revert "powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled"

From: Michael Ellerman <patch-notifications@ellerman.id.au>
To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] Revert "powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled"
Date: Mon,  6 Apr 2020 23:05:51 +1000 (AEST)	[thread overview]
Message-ID: <48wrPr2x9bz9sRY@ozlabs.org> (raw)
In-Reply-To: <20200402120401.1115883-1-npiggin@gmail.com>

On Thu, 2020-04-02 at 12:04:01 UTC, Nicholas Piggin wrote:
> This reverts commit ebb37cf3ffd39fdb6ec5b07111f8bb2f11d92c5f.
> 
> That commit does not play well with soft-masked irq state manipulations
> in idle, interrupt replay, and possibly others due to tracing code
> sometimes using irq_work_queue (e.g., in trace_hardirqs_on()). That
> can cause PACA_IRQ_DEC to become set when it is not expected, and be
> ignored or cleared or cause warnings.
> 
> The net result seems to be missing an irq_work until the next timer
> interrupt in the worst case which is usually not going to be noticed,
> however it could be a long time if the tick is disabled, which is
> agains the spirit of irq_work and might cause real problems.
> 
> The idea is still solid, but it would need more work. It's not really
> clear if it would be worth added complexity, so revert this for now
> (not a straight revert, but replace with a comment explaining why we
> might see interrupts happening, and gives git blame something to find).
> 
> Fixes: ebb37cf3ffd3 ("powerpc/64: irq_work avoid interrupt when called with hardware irqs enabled")
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/abc3fce76adbdfa8f87272c784b388cd20b46049

cheers