Date: Tue, 30 May 2023 13:48:57 +0000
From: Eli Cohen <elic@...dia.com>
To: Chuck Lever III <chuck.lever@...cle.com>, Shay Drory <shayd@...dia.com>
CC: Leon Romanovsky <leon@...nel.org>, Saeed Mahameed <saeedm@...dia.com>,
	linux-rdma <linux-rdma@...r.kernel.org>, "open list:NETWORKING [GENERAL]"
	<netdev@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: RE: system hang on start-up (mlx5?)

> From: Chuck Lever III <chuck.lever@...cle.com>
> Sent: Tuesday, 30 May 2023 16:28
> To: Eli Cohen <elic@...dia.com>
> Cc: Leon Romanovsky <leon@...nel.org>; Saeed Mahameed
> <saeedm@...dia.com>; linux-rdma <linux-rdma@...r.kernel.org>; open
> list:NETWORKING [GENERAL] <netdev@...r.kernel.org>; Thomas Gleixner
> <tglx@...utronix.de>
> Subject: Re: system hang on start-up (mlx5?)
> 
> 
> 
> > On May 30, 2023, at 9:09 AM, Chuck Lever III <chuck.lever@...cle.com>
> wrote:
> >
> >> On May 29, 2023, at 5:20 PM, Thomas Gleixner <tglx@...utronix.de>
> wrote:
> >>
> >> On Sat, May 27 2023 at 20:16, Chuck Lever, III wrote:
> >>>> On May 7, 2023, at 1:31 AM, Eli Cohen <elic@...dia.com> wrote:
> >>> I can boot the system with mlx5_core deny-listed. I log in, remove
> >>> mlx5_core from the deny list, and then "modprobe mlx5_core" to
> >>> reproduce the issue while the system is running.
> >>>
> >>> May 27 15:47:45 manet.1015granger.net kernel: mlx5_core 0000:81:00.0:
> firmware version: 16.35.2000
> >>> May 27 15:47:45 manet.1015granger.net kernel: mlx5_core 0000:81:00.0:
> 126.016 Gb/s available PCIe bandwidth (8.0 GT/s PCIe x16 link)
> >>> May 27 15:47:46 manet.1015granger.net kernel: mlx5_irq_alloc:
> pool=ffff9a3718e56180 i=0 af_desc=ffffb6c88493fc90
> >>> May 27 15:47:46 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a3aefcf0f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:46 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a3aefcf0f60 end=236
> >>> May 27 15:47:46 manet.1015granger.net kernel: mlx5_core 0000:81:00.0:
> Port module event: module 0, Cable plugged
> >>> May 27 15:47:46 manet.1015granger.net kernel: mlx5_irq_alloc:
> pool=ffff9a3718e56180 i=1 af_desc=ffffb6c88493fc60
> >>> May 27 15:47:46 manet.1015granger.net kernel: mlx5_core 0000:81:00.0:
> mlx5_pcie_event:301:(pid 10): PCIe slot advertised sufficient power (27W).
> >>> May 27 15:47:46 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a36efcf0f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a36efcf0f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a36efd30f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a36efd30f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a3aefc30f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a3aefc30f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a3aefc70f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a3aefc70f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a3aefd30f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a3aefd30f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffff9a3aefd70f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->alloc_map=ffff9a3aefd70f60 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: matrix_alloc_area: m-
> >scratch_map=ffff9a33801990b0 cm->managed_map=ffffffffb9ef3f80 m-
> >system_map=ffff9a33801990d0 end=236
> >>> May 27 15:47:47 manet.1015granger.net kernel: BUG: unable to handle
> page fault for address: ffffffffb9ef3f80
> >>>
> >>> ###
> >>>
> >>> The fault address is the cm->managed_map for one of the CPUs.
> >>
> >> That does not make any sense at all. The irq matrix is initialized via:
> >>
> >> irq_alloc_matrix()
> >> m = kzalloc(sizeof(matric);
> >> m->maps = alloc_percpu(*m->maps);
> >>
> >> So how is any per CPU map which got allocated there supposed to be
> >> invalid (not mapped):
> >>
> >>> May 27 15:47:47 manet.1015granger.net kernel: BUG: unable to handle
> page fault for address: ffffffffb9ef3f80
> >>> May 27 15:47:47 manet.1015granger.net kernel: #PF: supervisor read
> access in kernel mode
> >>> May 27 15:47:47 manet.1015granger.net kernel: #PF: error_code(0x0000)
> - not-present page
> >>> May 27 15:47:47 manet.1015granger.net kernel: PGD 54ec19067 P4D
> 54ec19067 PUD 54ec1a063 PMD 482b83063 PTE 800ffffab110c062
> >>
> >> But if you look at the address: 0xffffffffb9ef3f80
> >>
> >> That one is bogus:
> >>
> >>    managed_map=ffff9a36efcf0f80
> >>    managed_map=ffff9a36efd30f80
> >>    managed_map=ffff9a3aefc30f80
> >>    managed_map=ffff9a3aefc70f80
> >>    managed_map=ffff9a3aefd30f80
> >>    managed_map=ffff9a3aefd70f80
> >>    managed_map=ffffffffb9ef3f80
> >>
> >> Can you spot the fail?
> >>
> >> The first six are in the direct map and the last one is in module map,
> >> which makes no sense at all.
> >
> > Indeed. The reason for that is that the affinity mask has bits
> > set for CPU IDs that are not present on my system.
> >
> > After bbac70c74183 ("net/mlx5: Use newer affinity descriptor")
> > that mask is set up like this:
> >
> > struct mlx5_irq *mlx5_ctrl_irq_request(struct mlx5_core_dev *dev)
> > {
> >        struct mlx5_irq_pool *pool = ctrl_irq_pool_get(dev);
> > -       cpumask_var_t req_mask;
> > +       struct irq_affinity_desc af_desc;
> >        struct mlx5_irq *irq;
> > -       if (!zalloc_cpumask_var(&req_mask, GFP_KERNEL))
> > -               return ERR_PTR(-ENOMEM);
> > -       cpumask_copy(req_mask, cpu_online_mask);
> > +       cpumask_copy(&af_desc.mask, cpu_online_mask);
> > +       af_desc.is_managed = false;
> 
> By the way, why is "is_managed" set to false?
> 
> This particular system is a NUMA system, and I'd like to be
> able to set IRQ affinity for the card. Since is_managed is
> set to false, writing to the /proc/irq files fails with EIO.
>
This is a control irq and is used for issuing configuration commands.

This commit:
commit c410abbbacb9b378365ba17a30df08b4b9eec64f
Author: Dou Liyang <douliyangs@...il.com>
Date:   Tue Dec 4 23:51:21 2018 +0800

    genirq/affinity: Add is_managed to struct irq_affinity_desc

explains why it should not be managed.
 
> 
> > Which normally works as you would expect. But for some historical
> > reason, I have CONFIG_NR_CPUS=32 on my system, and the
> > cpumask_copy() misbehaves.
> >
> > If I correct mlx5_ctrl_irq_request() to clear @af_desc before the
> > copy, this crash goes away. But mlx5_core crashes during a later
> > part of its init, in cpu_rmap_update(). cpu_rmap_update() does
> > exactly the same thing (for_each_cpu() on an affinity mask created
> > by copying), and crashes in a very similar fashion.
> >
> > If I set CONFIG_NR_CPUS to a larger value, like 512, the problem
> > vanishes entirely, and "modprobe mlx5_core" works as expected.
> >
> > Thus I think the problem is with cpumask_copy() or for_each_cpu()
> > when NR_CPUS is a small value (the default is 8192).
> >
> >
> >> Can you please apply the debug patch below and provide the output?
> >>
> >> Thanks,
> >>
> >>       tglx
> >> ---
> >> --- a/kernel/irq/matrix.c
> >> +++ b/kernel/irq/matrix.c
> >> @@ -51,6 +51,7 @@ struct irq_matrix {
> >>  unsigned int alloc_end)
> >> {
> >> struct irq_matrix *m;
> >> + unsigned int cpu;
> >>
> >> if (matrix_bits > IRQ_MATRIX_BITS)
> >> return NULL;
> >> @@ -68,6 +69,8 @@ struct irq_matrix {
> >> kfree(m);
> >> return NULL;
> >> }
> >> + for_each_possible_cpu(cpu)
> >> + pr_info("ALLOC: CPU%03u: %016lx\n", cpu, (unsigned
> long)per_cpu_ptr(m->maps, cpu));
> >> return m;
> >> }
> >>
> >> @@ -215,6 +218,8 @@ int irq_matrix_reserve_managed(struct ir
> >> struct cpumap *cm = per_cpu_ptr(m->maps, cpu);
> >> unsigned int bit;
> >>
> >> + pr_info("RESERVE MANAGED: CPU%03u: %016lx\n", cpu, (unsigned
> long)cm);
> >> +
> >> bit = matrix_alloc_area(m, cm, 1, true);
> >> if (bit >= m->alloc_end)
> >> goto cleanup;
> >
> > --
> > Chuck Lever
> 
> 
> --
> Chuck Lever
> 

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