On 11.11.2018 20:13, Oleksandr Natalenko wrote:
Hi.
I was just curious about PREEMPT_RT and decided to give it a (small)
shot on my laptop. As a safety measure, I've enabled netconsole to
catch all the weird stuff that can pop up, and immediately it indeed
did… in the netconsole code itself (irony):
===
[ 64.018949] WARNING: CPU: 0 PID: 1204 at net/core/netpoll.c:372
netpoll_send_udp+0x3e8/0x3ef
…
[ 64.019057] CPU: 0 PID: 1204 Comm: bash Not tainted 4.19.0-ig1 #1
[ 64.019058] Hardware name: Dell Inc. Vostro 3360/0F5DWF,
BIOS A18 09/25/2013
[ 64.019063] RIP: 0010:netpoll_send_udp+0x3e8/0x3ef
[
64.019066] Code: dd ff ff 41 ba 86 dd ff ff 49 2b 96 d0 00 00 00 66 41
89 96 c6 00 00 00 66 44 89 48 0c 66 45 89 96 c0 00 00 00 e9
93 fe ff ff <0f> 0b e9 40 fc ff ff 0f 1f 44 00 00 53 0f b7 57 42 48 89
fb 48 8b
[ 64.019068] RSP: 0018:ffffaa6743f87c98 EFLAGS: 00010202
[ 64.019070] RAX: 0000000000000292 RBX: 0000000000000014 RCX:
0000000000000028
[ 64.019072] RDX: 0000000000000014 RSI: ffffffffb1e6a300 RDI:
ffff95973d905668
[ 64.019073] RBP: ffffaa6743f87cd8 R08: ffffffffc11f6ba0 R09:
0000000000000000
[ 64.019075] R10: 0000000000000008 R11: 0000000000000000 R12:
00000000000003e8
[ 64.019076] R13: ffff95973d905668 R14: 0000000000000014 R15:
ffff95973d905668
[ 64.019079] FS: 00007f2f8b809b80(0000) GS:ffff95976f000000(0000)
knlGS:0000000000000000
[ 64.019081] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 64.019083] CR2: 000055b8e126fbc8 CR3: 0000000415440006 CR4:
00000000001606f0
[ 64.019084] Call Trace:
[ 64.019098] write_msg+0xd1/0xe0 [netconsole]
[ 64.019107] console_unlock.part.6+0x55b/0x5a0
[ 64.019115] ? _raw_spin_unlock_irqrestore+0x20/0x60
[ 64.019120] vprintk_emit+0x16a/0x1a0
[ 64.019125] printk_emit+0x44/0x5b
[ 64.019130] ? _raw_spin_trylock+0x13/0x80
[ 64.019134] devkmsg_write.cold.16+0x21/0x4e
[ 64.019140] __vfs_write+0x136/0x1a0
[ 64.019145] vfs_write+0xa9/0x1a0
[ 64.019149] ksys_write+0x52/0xc0
[ 64.019156] do_syscall_64+0x5b/0x170
[ 64.019160] entry_SYSCALL_64_after_hwframe+0x44/0xa9
…
===
This is a v4.19.1-rt3-based kernel.
The WARN_ON() is:
362 void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
363 {
…
372 WARN_ON_ONCE(!irqs_disabled());
…
If that matters, I have "threadirqs" passed to the kernel.
Netconsole seems to work even after this warning. Is this OK/expected?
Thanks.
Oh, I see that write_msg() calls netpoll_send_udp() under
spin_lock_irqsave(), but in PREEMPT_RT this, AFAIK, does not disable
interrupts.
So, the real question here is whether the interrupts should be indeed
disabled. And if so, -rt should replace spin_lock_irqsave() call there
with what? local_irq_save()? and get rid of the warning?
--
Oleksandr Natalenko (post-factum)
