go: crypto/rand: warn about very slow (60-second) /dev/urandom reads

What version of Go are you using (go version)?

go version go1.9.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

This issue shows itself on linux/arm

What did you do?

Compile this program and run it on a linux/arm server.

What did you expect to see?

If it works it should produce output similar to this

go version devel +0ba4eba864 Mon Nov 6 08:37:30 2017 +0000
Status: 401: 401 Unauthorized
Body:
{
  "code": "missing_auth_token",
  "message": "Missing authorization token",
  "status": 401
}

What did you see instead?

However when compiled with go1.9 or go-tip it hangs indefinitely on some ARM servers. It works fine with go-1.8.

This issue came up as part of https://github.com/ncw/rclone/issues/1794

I haven’t managed to replicate the hang on my raspberry Pi 3, but both @HptmHavoc and @freespace have on scaleway arm servers using different kernels.

I’m not 100% sure what is going on but it is clearly a regression.

---

From the above @freespace wrote:

$ time ./b2get-go-tip
go version devel +0ba4eba864 Mon Nov 6 08:37:30 2017 +0000
^C

real    0m7.447s
user    0m0.020s
sys     0m0.010s
steve@mercury:~/tmp/b2get
$ time ./b2get-go1.9.2
go version go1.9.2
^C

real    0m10.927s
user    0m0.030s
sys     0m0.010s
steve@mercury:~/tmp/b2get
$ time ./b2get-go1.8.3
go version go1.8.3
Status: 401: 401 Unauthorized
Body:
{
  "code": "missing_auth_token",
  "message": "Missing authorization token",
  "status": 401
}
real    0m0.842s
user    0m0.230s
sys     0m0.010s

$ uname -a
Linux mercury 4.5.7-std-4 #1 SMP Tue Jul 12 11:00:06 UTC 2016 armv7l GNU/Linux

$ cat /proc/cpuinfo | head -20
processor       : 0
model name      : ARMv7 Processor rev 2 (v7l)
BogoMIPS        : 50.00
Features        : half thumb fastmult vfp edsp thumbee vfpv3 tls idiva idivt vfpd32 lpae
CPU implementer : 0x56
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0x584
CPU revision    : 2

...
<snip>
...
Hardware        : Marvell Armada 370/XP (Device Tree)
Revision        : 0000
Serial          : 0000000000000000

Mine is a scaleway arm server.

---

And from the above @HptmHavoc wrote:

Here pretty much the same, also a scaleway arm server.

time ./b2get-go-tip 
go version devel +0ba4eba864 Mon Nov 6 08:37:30 2017 +0000
^CCommand terminated by signal 2
real	0m 34.52s
user	0m 0.00s
sys	0m 0.01s

time ./b2get-go1.9.2 
go version go1.9.2
^CCommand terminated by signal 2
real	3m 2.82s
user	0m 0.02s
sys	0m 0.00s

time ./b2get-go1.8.3 
go version go1.8.3
Status: 401: 401 Unauthorized
Body:
{
  "code": "missing_auth_token",
  "message": "Missing authorization token",
  "status": 401
}real	0m 0.78s
user	0m 0.16s
sys	0m 0.01s

$ uname -a
Linux scw-553c2c 4.4.96-mainline-rev1 #1 SMP Thu Nov 2 11:27:34 UTC 2017 armv7l Linux

$ cat /proc/cpuinfo | head -20
processor	: 0
model name	: ARMv7 Processor rev 2 (v7l)
BogoMIPS	: 50.00
Features	: half thumb fastmult vfp edsp thumbee vfpv3 tls idiva idivt vfpd32 lpae 
CPU implementer	: 0x56
CPU architecture: 7
CPU variant	: 0x2
CPU part	: 0x584
CPU revision	: 2

...
<snip>
...

Hardware	: Marvell Armada 370/XP (Device Tree)
Revision	: 0000
Serial		: 0000000000000000