On Fri, 9 Oct 2020 02:46:09 +0300
Vladimir Oltean <olte...@gmail.com> wrote:
> On Thu, Oct 08, 2020 at 05:27:49PM +0100, John Keeping wrote:
> > With threadirqs, stmmac_interrupt() is called on a thread with hardirqs
> > enabled so we cannot call __napi_schedule_irqoff(). Under lockdep it
> > leads to:
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 285 at kernel/softirq.c:598
> > __raise_softirq_irqoff+0x6c/0x1c8
> > IRQs not disabled as expected
> > Modules linked in: brcmfmac hci_uart btbcm cfg80211 brcmutil
> > CPU: 0 PID: 285 Comm: irq/41-eth0 Not tainted 5.4.69-rt39 #1
> > Hardware name: Rockchip (Device Tree)
> > [<c0110d3c>] (unwind_backtrace) from [<c010c284>] (show_stack+0x10/0x14)
> > [<c010c284>] (show_stack) from [<c0855504>] (dump_stack+0xa8/0xe0)
> > [<c0855504>] (dump_stack) from [<c0120a9c>] (__warn+0xe0/0xfc)
> > [<c0120a9c>] (__warn) from [<c0120e80>] (warn_slowpath_fmt+0x7c/0xa4)
> > [<c0120e80>] (warn_slowpath_fmt) from [<c01278c8>]
> > (__raise_softirq_irqoff+0x6c/0x1c8)
> > [<c01278c8>] (__raise_softirq_irqoff) from [<c056bccc>]
> > (stmmac_interrupt+0x388/0x4e0)
> > [<c056bccc>] (stmmac_interrupt) from [<c0178714>]
> > (irq_forced_thread_fn+0x28/0x64)
> > [<c0178714>] (irq_forced_thread_fn) from [<c0178924>]
> > (irq_thread+0x124/0x260)
> > [<c0178924>] (irq_thread) from [<c0142ee8>] (kthread+0x154/0x164)
> > [<c0142ee8>] (kthread) from [<c01010bc>] (ret_from_fork+0x14/0x38)
> > Exception stack(0xeb7b5fb0 to 0xeb7b5ff8)
> > 5fa0: 00000000 00000000 00000000
> > 00000000
> > 5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> > 00000000
> > 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > irq event stamp: 48
> > hardirqs last enabled at (50): [<c085c200>] prb_unlock+0x7c/0x8c
> > hardirqs last disabled at (51): [<c085c0dc>] prb_lock+0x58/0x100
> > softirqs last enabled at (0): [<c011e770>] copy_process+0x550/0x1654
> > softirqs last disabled at (25): [<c01786ec>]
> > irq_forced_thread_fn+0x0/0x64
> > ---[ end trace 0000000000000002 ]---
> >
> > Use __napi_schedule() instead which will save & restore the interrupt
> > state.
> >
> > Fixes: 4ccb45857c2c ("net: stmmac: Fix NAPI poll in TX path when in
> > multi-queue")
> > Signed-off-by: John Keeping <j...@metanate.com>
> > ---
>
> Don't get me wrong, this is so cool that the new lockdep warning is really
> helping out finding real bugs, but the patch that adds that warning
> (https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=cdabce2e3dff7e4bcef73473987618569d178af3)
> isn't in 5.4.69-rt39, is it?
No, it's not, although I would have saved several days debugging if it
was! I backported the lockdep warning to prove that it caught this
issue.
The evidence it is possible to see on vanilla 5.4.x is:
$ trace-cmd report -l
irq/43-e-280 0....2 74.017658: softirq_raise: vec=3
[action=NET_RX]
Note the missing "d" where this should be "0d...2" to indicate hardirqs
disabled.
Regards,
John
