linux-kernel - Re: [PATCH] Revert "seqlock: lockdep assert non-preemptibility on seqcount

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Date:   Mon, 10 Aug 2020 12:05:02 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
Cc:     bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        linux@...ck-us.net, mingo@...hat.com, paulmck@...nel.org,
        peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
        will@...nel.org
Subject: Re: [PATCH] Revert "seqlock: lockdep assert non-preemptibility on
 seqcount_t write"

On Mon, Aug 10, 2020 at 11:54:28AM +0200, Ahmed S. Darwish wrote:
> This reverts commit 859247d39fb008ea812e8f0c398a58a20c12899e.
> 
> Current implementation of lockdep_assert_preemption_disabled() uses
> per-CPU variables, which was done to untangle the existing
> seqlock.h<=>sched.h 'current->' task_struct circular dependency.
> 
> Using per-CPU variables did not fully untangle the dependency for
> various non-x86 architectures though, resulting in multiple broken
> builds. For the affected architectures, raw_smp_processor_id() led
> back to 'current->', thus having the original seqlock.h<=>sched.h
> dependency in full-effect.
> 
> For now, revert adding lockdep_assert_preemption_disabled() to
> seqlock.h.
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Link: https://lkml.kernel.org/r/20200808232122.GA176509@roeck-us.net
> Link: https://lkml.kernel.org/r/20200810085954.GA1591892@kroah.com
> References: Commit a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
> Signed-off-by: Ahmed S. Darwish <a.darwish@...utronix.de>

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Even after this, there are still some build errors on arm32, but I don't
think they are due to this change:

	ERROR: modpost: "__aeabi_uldivmod" [drivers/net/ethernet/sfc/sfc.ko] undefined!
	ERROR: modpost: "__bad_udelay" [drivers/net/ethernet/aquantia/atlantic/atlantic.ko] undefined!

thanks,

greg k-h