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

[Justin He]

> -----Original Message-----
> From: Prabhakar Kushwaha <prabhakar.pkin@xxxxxxxxx>
> Sent: Monday, July 19, 2021 10:51 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 Justin,
> 
> On Mon, Jul 19, 2021 at 6:47 PM Justin He <Justin.He@xxxxxxx> wrote:
> >
> > 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
> 
> I agree till here.
> 
> >   if (cnt >= max_retries) {
> > ...
> >     return -EAGAIN; <-- here returns -EAGAIN without invoking bh unlock
> >   }
> >
> 
> Because of break, cnt has not been increased.
>    - cnt is still less than max_retries.
>   - if (cnt >= max_retries) will not be *true*, leading to spin_unlock_bh().
> Hence pairing completed.

Sorry, indeed. Let me check other possibilities.
@David S. Miller Sorry for the inconvenience, could you please revert it
in netdev tree?

Apologies again.

--
Cheers,
Justin (Jia He)