RE: [PATCH] qed: fix possible unpaired spin_{un}lock_bh in _qed_mcp_cmd_and_union()

[Justin He]

Hi Prabhakar

> -----Original Message-----
> From: Prabhakar Kushwaha <prabhakar.pkin@xxxxxxxxx>
> Sent: Monday, July 19, 2021 6:36 PM
> To: Justin He <Justin.He@xxxxxxx>
> Cc: Ariel Elior <aelior@xxxxxxxxxxx>; GR-everest-linux-l2@xxxxxxxxxxx;
> David S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx; Linux Kernel Mailing List <linux-
> kernel@xxxxxxxxxxxxxxx>; nd <nd@xxxxxxx>; Shai Malin <malin1024@xxxxxxxxx>;
> Shai Malin <smalin@xxxxxxxxxxx>; Prabhakar Kushwaha <pkushwaha@xxxxxxxxxxx>
> Subject: Re: [PATCH] qed: fix possible unpaired spin_{un}lock_bh in
> _qed_mcp_cmd_and_union()
> 
> Hi Jia,
> 
> On Thu, Jul 15, 2021 at 2:28 PM Jia He <justin.he@xxxxxxx> wrote:
> >
> > Liajian reported a bug_on hit on a ThunderX2 arm64 server with FastLinQ
> > QL41000 ethernet controller:
> >  BUG: scheduling while atomic: kworker/0:4/531/0x00000200
> >   [qed_probe:488()]hw prepare failed
> >   kernel BUG at mm/vmalloc.c:2355!
> >   Internal error: Oops - BUG: 0 [#1] SMP
> >   CPU: 0 PID: 531 Comm: kworker/0:4 Tainted: G W 5.4.0-77-generic #86-
> Ubuntu
> >   pstate: 00400009 (nzcv daif +PAN -UAO)
> >  Call trace:
> >   vunmap+0x4c/0x50
> >   iounmap+0x48/0x58
> >   qed_free_pci+0x60/0x80 [qed]
> >   qed_probe+0x35c/0x688 [qed]
> >   __qede_probe+0x88/0x5c8 [qede]
> >   qede_probe+0x60/0xe0 [qede]
> >   local_pci_probe+0x48/0xa0
> >   work_for_cpu_fn+0x24/0x38
> >   process_one_work+0x1d0/0x468
> >   worker_thread+0x238/0x4e0
> >   kthread+0xf0/0x118
> >   ret_from_fork+0x10/0x18
> >
> > In this case, qed_hw_prepare() returns error due to hw/fw error, but in
> > theory work queue should be in process context instead of interrupt.
> >
> > The root cause might be the unpaired spin_{un}lock_bh() in
> > _qed_mcp_cmd_and_union(), which causes botton half is disabled
> incorrectly.
> >
> > Reported-by: Lijian Zhang <Lijian.Zhang@xxxxxxx>
> > Signed-off-by: Jia He <justin.he@xxxxxxx>
> > ---
> 
> This patch is adding additional spin_{un}lock_bh().
> Can you please enlighten about the exact flow causing this unpaired
> spin_{un}lock_bh.
> 
For instance:
_qed_mcp_cmd_and_union()
  In while loop
    spin_lock_bh()
    qed_mcp_has_pending_cmd() (assume false), will break the loop
  if (cnt >= max_retries) {
...
    return -EAGAIN; <-- here returns -EAGAIN without invoking bh unlock 
  }

> Also,
> as per description, looks like you are not sure actual the root-cause.
> does this patch really solved the problem?

I don't have that ThunderX2 to verify the patch.
But I searched all the spin_lock/unlock_bh and spin_lock_irqsave/irqrestore
under driver/.../qlogic, this is the only problematic point I could figure
out. And this might be possible code path of qed_probe().

--
Cheers,
Justin (Jia He)