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

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Date:   Tue, 18 Aug 2020 18:51:18 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Guenter Roeck <linux@...ck-us.net>,
        Mark Starovoytov <mstarovoitov@...vell.com>,
        Igor Russkikh <irusskikh@...vell.com>,
        "David S. Miller" <davem@...emloft.net>
cc:     Greg KH <gregkh@...uxfoundation.org>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        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, 10 Aug 2020 07:10:32 -0700, Guenter Roeck said:
> > 	ERROR: modpost: "__bad_udelay" [drivers/net/ethernet/aquantia/atlantic/atlantic.ko] undefined!
> > 
>
> I don't think that is new. If anything, it is surprising that builds don't fail more
> widely because of it. AFAICS it was introduced back in 2018 (a hot 50-ms delay loop
> really isn't such a good idea).

Well...it wasn't broken in next-20200720.  A bit of poking with nm,
and building hw_atl/hw_atl_b0.s, it looks like the culprit is this commit:

commit 8dcf2ad39fdb2d183b7bd4307c837713e3150b9a
Author: Mark Starovoytov <mstarovoitov@...vell.com>
Date:   Mon Jul 20 21:32:44 2020 +0300

    net: atlantic: add hwmon getter for MAC temperature

specifically this chunk around line 1634 of hw_atl/hw_atl_b0.c:


+       err = readx_poll_timeout_atomic(hw_atl_b0_ts_ready_and_latch_high_get,
+                                       self, val, val == 1, 10000U, 500000U);

And doing a 'git revert' makes the build work....