linux-kernel - Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu

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Message-ID: <Y0lCr9f0fekMgASN@gondor.apana.org.au>
Date:   Fri, 14 Oct 2022 19:06:23 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        kernelci-results@...ups.io, bot@...nelci.org,
        gtucker@...labora.com, linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of
 cpu_relax()

On Mon, Oct 10, 2022 at 09:06:07AM -0600, Jason A. Donenfeld wrote:
> Rather than busy looping, yield back to the scheduler and sleep for a
> bit in the event that there's no data. This should hopefully prevent the
> stalls that Mark reported:
> 
> <6>[    3.362859] Freeing initrd memory: 16196K
> <3>[   23.160131] rcu: INFO: rcu_sched self-detected stall on CPU
> <3>[   23.166057] rcu:  0-....: (2099 ticks this GP) idle=03b4/1/0x40000002 softirq=28/28 fqs=1050
> <4>[   23.174895]       (t=2101 jiffies g=-1147 q=2353 ncpus=4)
> <4>[   23.180203] CPU: 0 PID: 49 Comm: hwrng Not tainted 6.0.0 #1
> <4>[   23.186125] Hardware name: BCM2835
> <4>[   23.189837] PC is at bcm2835_rng_read+0x30/0x6c
> <4>[   23.194709] LR is at hwrng_fillfn+0x71/0xf4
> <4>[   23.199218] pc : [<c07ccdc8>]    lr : [<c07cb841>]    psr: 40000033
> <4>[   23.205840] sp : f093df70  ip : 00000000  fp : 00000000
> <4>[   23.211404] r10: c3c7e800  r9 : 00000000  r8 : c17e6b20
> <4>[   23.216968] r7 : c17e6b64  r6 : c18b0a74  r5 : c07ccd99  r4 : c3f171c0
> <4>[   23.223855] r3 : 000fffff  r2 : 00000040  r1 : c3c7e800  r0 : c3f171c0
> <4>[   23.230743] Flags: nZcv  IRQs on  FIQs on  Mode SVC_32  ISA Thumb  Segment none
> <4>[   23.238426] Control: 50c5387d  Table: 0020406a  DAC: 00000051
> <4>[   23.244519] CPU: 0 PID: 49 Comm: hwrng Not tainted 6.0.0 #1
> 
> Link: https://lore.kernel.org/all/Y0QJLauamRnCDUef@sirena.org.uk/
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> I haven't tested this. Somebody with access to that kernel CI infra that
> triggered this will need to test.
> 
>  drivers/char/hw_random/bcm2835-rng.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt