On Mon, 26 Jul 2004, Robert Olsson wrote:
> Pasi Sjoholm writes:
> > Pid: 2, comm: ksoftirqd/0
> > EIP: 0060:[<e0871224>] CPU: 0
> > EIP is at rtl8139_poll+0xb4/0x100 [8139too]
> > EFLAGS: 00000247 Not tainted (2.6.7-mm7)
> > EAX: ffffe000 EBX: 00000040 ECX: df4824f8 EDX: c0441978
> > ESI: df482400 EDI: e0868000 EBP: dff85f80 DS: 007b ES: 007b
> > CR0: 8005003b CR2: b7c5a000 CR3: 1fafd000 CR4: 000006d0
> > [<c0119580>] ksoftirqd+0x0/0xc0
> > [<c02c5f3a>] net_rx_action+0x6a/0x110
> > [<c01191a9>] __do_softirq+0xa9/0xb0
> > [<c01191d7>] do_softirq+0x27/0x30
> > [<c01195e8>] ksoftirqd+0x68/0xc0
> > [<c01277e5>] kthread+0xa5/0xb0
> > [<c0127740>] kthread+0x0/0xb0
> > [<c0102111>] kernel_thread_helper+0x5/0x14
> > --
> > I'm not a kernel expert but it would seem that ksoftirqd is in some sort a
> > loop because I didn't get any "printk("%s wakes ksoftirqd\n",
> > current->comm);"-lines.
> Hello!
Hur är läget Robert?-)
> This looks very much like the problem we see when doing route DoS testing
> with Alexey.
Hmm, at least it sounds like same problem and in both situations network
interface is kept busy.
> In summary: High softirq loads can totally kill userland. The reason is that
> do_softirq() is run from many places hard interrupts, local_bh_enable etc
> and bypasses the ksoftirqd protection. It just been discussed at OLS with
> Andrea and Dipankar and others. Current RCU suffers from this problem as
> well.
Ok, this explanation makes sense and my point of view I think this is
quite critical problem if you can "crash" linux kernel just sending enough
packets to network interface for an example.
> I've experimented some code to defer softirq's to ksoftirqd after a time as
> well as deferring all softirq's to ksoftirqd. Andrea had some ideas as well
> as Ingo.
I would be more than glad to help you in testing if you want to publish
some patches.
--
Pasi Sjöholm
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