[PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu

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* [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax()
       [not found] <Y0QjkjU4bsOHWFOd@sirena.org.uk>
@ 2022-10-10 15:06 ` Jason A. Donenfeld
  2022-10-10 15:37   ` Jason A. Donenfeld
                     ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Jason A. Donenfeld @ 2022-10-10 15:06 UTC (permalink / raw)
  To: Mark Brown, Florian Fainelli, Jason A. Donenfeld,
	Dominik Brodowski, Herbert Xu, kernelci-results, bot, gtucker,
	linux-arm-kernel, linux-rpi-kernel, bcm-kernel-feedback-list,
	linux-crypto, linux-kernel

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@zx2c4.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(-)

diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
index e7dd457e9b22..e98fcac578d6 100644
--- a/drivers/char/hw_random/bcm2835-rng.c
+++ b/drivers/char/hw_random/bcm2835-rng.c
@@ -71,7 +71,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
 	while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
 		if (!wait)
 			return 0;
-		cpu_relax();
+		hwrng_msleep(rng, 1000);
 	}
 
 	num_words = rng_readl(priv, RNG_STATUS) >> 24;
-- 
2.37.3


^ permalink raw reply related	[flat|nested] 4+ messages in thread

* Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax()
  2022-10-10 15:06 ` [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax() Jason A. Donenfeld
@ 2022-10-10 15:37   ` Jason A. Donenfeld
  2022-10-10 22:05   ` Florian Fainelli
  2022-10-14 11:06   ` Herbert Xu
  2 siblings, 0 replies; 4+ messages in thread
From: Jason A. Donenfeld @ 2022-10-10 15:37 UTC (permalink / raw)
  To: Mark Brown, Florian Fainelli, Dominik Brodowski, Herbert Xu,
	kernelci-results, bot, gtucker, linux-arm-kernel,
	linux-rpi-kernel, bcm-kernel-feedback-list, linux-crypto,
	linux-kernel

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@zx2c4.com>
> ---
> I haven't tested this. Somebody with access to that kernel CI infra that
> triggered this will need to test.

So I succeeded at testing this, sort of. I was able to reproduce the
hang on a CONFIG_PREEMPT=n kernel with this diff:

diff --git a/drivers/net/wireguard/main.c b/drivers/net/wireguard/main.c
index ee4da9ab8013..19e1186f0db0 100644
--- a/drivers/net/wireguard/main.c
+++ b/drivers/net/wireguard/main.c
@@ -15,12 +15,29 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/genetlink.h>
+#include <linux/hw_random.h>
 #include <net/rtnetlink.h>

+static int derp_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	if (wait) {
+		for (;;)
+			cpu_relax();
+	}
+	return 0;
+}
+
+static struct hwrng derp_ops = {
+	.name = "flurpderp",
+	.read = derp_rng_read,
+};
+
 static int __init wg_mod_init(void)
 {
 	int ret;

+	hwrng_register(&derp_ops);
+
 	ret = wg_allowedips_slab_init();
 	if (ret < 0)
 		goto err_allowedips;


Next, I changed the cpu_relax() into hwrng_msleep(), as this patch does:

diff --git a/drivers/net/wireguard/main.c b/drivers/net/wireguard/main.c
index ee4da9ab8013..19e1186f0db0 100644
--- a/drivers/net/wireguard/main.c
+++ b/drivers/net/wireguard/main.c
@@ -15,12 +15,29 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/genetlink.h>
+#include <linux/hw_random.h>
 #include <net/rtnetlink.h>

+static int derp_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	if (wait) {
+		for (;;)
+			hwrng_msleep(rng, 1000);
+	}
+	return 0;
+}
+
+static struct hwrng derp_ops = {
+	.name = "flurpderp",
+	.read = derp_rng_read,
+};
+
 static int __init wg_mod_init(void)
 {
 	int ret;

+	hwrng_register(&derp_ops);
+
 	ret = wg_allowedips_slab_init();
 	if (ret < 0)
 		goto err_allowedips;

And then the problem went away.

So I think this patch is a good one.

Jason

^ permalink raw reply related	[flat|nested] 4+ messages in thread

* Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax()
  2022-10-10 15:06 ` [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax() Jason A. Donenfeld
  2022-10-10 15:37   ` Jason A. Donenfeld
@ 2022-10-10 22:05   ` Florian Fainelli
  2022-10-14 11:06   ` Herbert Xu
  2 siblings, 0 replies; 4+ messages in thread
From: Florian Fainelli @ 2022-10-10 22:05 UTC (permalink / raw)
  To: Jason A. Donenfeld, Mark Brown, Florian Fainelli,
	Dominik Brodowski, Herbert Xu, kernelci-results, bot, gtucker,
	linux-arm-kernel, linux-rpi-kernel, bcm-kernel-feedback-list,
	linux-crypto, linux-kernel

On 10/10/22 08:06, 'Jason A. Donenfeld' via BCM-KERNEL-FEEDBACK-LIST,PDL 
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@zx2c4.com>

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax()
  2022-10-10 15:06 ` [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax() Jason A. Donenfeld
  2022-10-10 15:37   ` Jason A. Donenfeld
  2022-10-10 22:05   ` Florian Fainelli
@ 2022-10-14 11:06   ` Herbert Xu
  2 siblings, 0 replies; 4+ messages in thread
From: Herbert Xu @ 2022-10-14 11:06 UTC (permalink / raw)
  To: Jason A. Donenfeld
  Cc: Mark Brown, Florian Fainelli, Dominik Brodowski, kernelci-results,
	bot, gtucker, linux-arm-kernel, linux-rpi-kernel,
	bcm-kernel-feedback-list, linux-crypto, linux-kernel

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@zx2c4.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@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

^ permalink raw reply	[flat|nested] 4+ messages in thread

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Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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     [not found] <Y0QjkjU4bsOHWFOd@sirena.org.uk>
2022-10-10 15:06 ` [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax() Jason A. Donenfeld
2022-10-10 15:37   ` Jason A. Donenfeld
2022-10-10 22:05   ` Florian Fainelli
2022-10-14 11:06   ` Herbert Xu

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