From: Eric Dumazet <edumazet@google.com>
To: Brian Starkey <brian.starkey@arm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"
Date: Thu, 17 Nov 2016 07:29:14 -0800 [thread overview]
Message-ID: <CANn89iKu+=7eD3MenkpfiwqkerwKkJJXonzHi=yiKc3o0A3p9w@mail.gmail.com> (raw)
In-Reply-To: <20161116210139.GB21156@e106950-lin.cambridge.arm.com>
[-- Attachment #1: Type: text/plain, Size: 3176 bytes --]
On Wed, Nov 16, 2016 at 1:01 PM, Brian Starkey <brian.starkey@arm.com> wrote:
> On Wed, Nov 16, 2016 at 10:49:06AM -0800, Eric Dumazet wrote:
>>
>> On Wed, Nov 16, 2016 at 10:01 AM, Brian Starkey <brian.starkey@arm.com>
>> wrote:
>>
>>>
>>> The smc91x driver does seem to have some trickiness around softirqs.
>>> I'm not familiar with net drivers, but I'll see if I can figure
>>> anything out there.
>>
>>
>> Oh this code looks ugly :(
>>
>> Do you have CONFIG_SMP=y or not ?
>
>
> Yeah CONFIG_SMP=y (and CONFIG_PREEMPT=y too, fwiw).
>
> I did try forcing it into the no-op locking (as though config SMP
> wasn't set), it didn't help (and it doesn't look like that would be
> safe with CONFIG_PREEMPT=y either).
>
> The bit in smc_hardware_send_pkt looks like skipping softirq
> invocation when there's already one running wouldn't give the same
> behaviour as before:
>
> if (!smc_special_trylock(&lp->lock, flags)) {
> netif_stop_queue(dev);
> tasklet_schedule(&lp->tx_task);
> return;
> }
>
> ... that said, I've no idea if that matters.
>
> Of course I also don't know if the network driver is even to blame :-(
>
I believe the problem is in SMC_WAIT_MMU_BUSY()
Could you try this patch ? (inlined and attached)
diff --git a/drivers/net/ethernet/smsc/smc91x.c
b/drivers/net/ethernet/smsc/smc91x.c
index 65077c77082a2f042117a0889c2b15099c58eae5..4ef653ae8564c6d2a5120cdaef12db1e1b218b39
100644
--- a/drivers/net/ethernet/smsc/smc91x.c
+++ b/drivers/net/ethernet/smsc/smc91x.c
@@ -229,19 +229,22 @@ static inline void PRINT_PKT(u_char *buf, int length) { }
* if at all, but let's avoid deadlocking the system if the hardware
* decides to go south.
*/
-#define SMC_WAIT_MMU_BUSY(lp) do { \
- if (unlikely(SMC_GET_MMU_CMD(lp) & MC_BUSY)) { \
- unsigned long timeout = jiffies + 2; \
- while (SMC_GET_MMU_CMD(lp) & MC_BUSY) { \
- if (time_after(jiffies, timeout)) { \
- netdev_dbg(dev, "timeout %s line %d\n", \
- __FILE__, __LINE__); \
- break; \
- } \
- cpu_relax(); \
- } \
- } \
-} while (0)
+static void SMC_WAIT_MMU_BUSY(struct smc_local *lp)
+{
+ unsigned long timeout = jiffies + 2;
+ unsigned int count = 10000;
+
+ while (SMC_GET_MMU_CMD(lp) & MC_BUSY) {
+ count--;
+ if (!count || time_after(jiffies, timeout)) {
+ netdev_dbg(lp->dev, "timeout %s line %d\n",
+ __FILE__, __LINE__);
+ break;
+ }
+ /* TODO : investigate using cond_resched() from allowed contexts */
+ cpu_relax();
+ }
+}
/*
[-- Attachment #2: patch2250.txt --]
[-- Type: text/plain, Size: 1266 bytes --]
diff --git a/drivers/net/ethernet/smsc/smc91x.c b/drivers/net/ethernet/smsc/smc91x.c
index 65077c77082a2f042117a0889c2b15099c58eae5..4ef653ae8564c6d2a5120cdaef12db1e1b218b39 100644
--- a/drivers/net/ethernet/smsc/smc91x.c
+++ b/drivers/net/ethernet/smsc/smc91x.c
@@ -229,19 +229,22 @@ static inline void PRINT_PKT(u_char *buf, int length) { }
* if at all, but let's avoid deadlocking the system if the hardware
* decides to go south.
*/
-#define SMC_WAIT_MMU_BUSY(lp) do { \
- if (unlikely(SMC_GET_MMU_CMD(lp) & MC_BUSY)) { \
- unsigned long timeout = jiffies + 2; \
- while (SMC_GET_MMU_CMD(lp) & MC_BUSY) { \
- if (time_after(jiffies, timeout)) { \
- netdev_dbg(dev, "timeout %s line %d\n", \
- __FILE__, __LINE__); \
- break; \
- } \
- cpu_relax(); \
- } \
- } \
-} while (0)
+static void SMC_WAIT_MMU_BUSY(struct smc_local *lp)
+{
+ unsigned long timeout = jiffies + 2;
+ unsigned int count = 10000;
+
+ while (SMC_GET_MMU_CMD(lp) & MC_BUSY) {
+ count--;
+ if (!count || time_after(jiffies, timeout)) {
+ netdev_dbg(lp->dev, "timeout %s line %d\n",
+ __FILE__, __LINE__);
+ break;
+ }
+ /* TODO : investigate using cond_resched() from allowed contexts */
+ cpu_relax();
+ }
+}
/*
next prev parent reply other threads:[~2016-11-17 17:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-16 13:55 Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job" Brian Starkey
2016-11-16 15:52 ` Eric Dumazet
2016-11-16 18:01 ` Brian Starkey
2016-11-16 18:49 ` Eric Dumazet
2016-11-16 21:01 ` Brian Starkey
2016-11-17 15:29 ` Eric Dumazet [this message]
2016-11-17 16:42 ` Brian Starkey
2016-11-18 0:40 ` Thomas Gleixner
2016-11-18 20:23 ` Brian Starkey
2016-11-22 10:33 ` Brian Starkey
2016-11-22 14:29 ` Eric Dumazet
2016-11-22 15:27 ` Brian Starkey
2016-11-22 16:09 ` Eric Dumazet
2016-11-23 18:21 ` Brian Starkey
2016-11-23 20:03 ` Eric Dumazet
2016-11-25 13:14 ` Brian Starkey
2017-02-06 18:46 ` Will Deacon
2017-02-06 18:49 ` Russell King - ARM Linux
2017-02-08 9:46 ` Will Deacon
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