Subject: Re: [PATCH mlx5-next 1/7] RDMA/mlx5: Don't set esc_size in user mr

From: Leon Romanovsky <[email-masked]>
Date: Tue, 12 Oct 2021 17:14:20 +0300

On Tue, Oct 12, 2021 at 11:04:33AM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 12, 2021 at 04:57:16PM +0300, Aharon Landau wrote:
> > 
> > On 10/12/2021 3:52 PM, Jason Gunthorpe wrote:
> > > On Tue, Oct 12, 2021 at 01:26:29PM +0300, Leon Romanovsky wrote:
> > > > From: Aharon Landau <[email-masked]>
> > > > 
> > > > reg_create() is used for user MRs only and should not set desc_size at
> > > > all. Attempt to set it causes to the following trace:
> > > > 
> > > > BUG: unable to handle page fault for address: 0000000800000000
> > > > PGD 0 P4D 0
> > > > Oops: 0000 [#1] SMP PTI
> > > > CPU: 5 PID: 890 Comm: ib_write_bw Not tainted 5.15.0-rc4+ #47
> > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> > > > RIP: 0010:mlx5_ib_dereg_mr+0x14/0x3b0 [mlx5_ib]
> > > > Code: 48 63 cd 4c 89 f7 48 89 0c 24 e8 37 30 03 e1 48 8b 0c 24 eb a0 90 0f 1f 44 00 00 41 56 41 55 41 54 55 53 48 89 fb 48 83 ec 30 <48> 8b 2f 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 8b 87 c8
> > > > RSP: 0018:ffff88811afa3a60 EFLAGS: 00010286
> > > > RAX: 000000000000001c RBX: 0000000800000000 RCX: 0000000000000000
> > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000800000000
> > > > RBP: 0000000800000000 R08: 0000000000000000 R09: c0000000fffff7ff
> > > > R10: ffff88811afa38f8 R11: ffff88811afa38f0 R12: ffffffffa02c7ac0
> > > > R13: 0000000000000000 R14: ffff88811afa3cd8 R15: ffff88810772fa00
> > > > FS:  00007f47b9080740(0000) GS:ffff88852cd40000(0000) knlGS:0000000000000000
> > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > CR2: 0000000800000000 CR3: 000000010761e003 CR4: 0000000000370ea0
> > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > > Call Trace:
> > > >   mlx5_ib_free_odp_mr+0x95/0xc0 [mlx5_ib]
> > > >   mlx5_ib_dereg_mr+0x128/0x3b0 [mlx5_ib]
> > > >   ib_dereg_mr_user+0x45/0xb0 [ib_core]
> > > >   ? xas_load+0x8/0x80
> > > >   destroy_hw_idr_uobject+0x1a/0x50 [ib_uverbs]
> > > >   uverbs_destroy_uobject+0x2f/0x150 [ib_uverbs]
> > > >   uobj_destroy+0x3c/0x70 [ib_uverbs]
> > > >   ib_uverbs_cmd_verbs+0x467/0xb00 [ib_uverbs]
> > > >   ? uverbs_finalize_object+0x60/0x60 [ib_uverbs]
> > > >   ? ttwu_queue_wakelist+0xa9/0xe0
> > > >   ? pty_write+0x85/0x90
> > > >   ? file_tty_write.isra.33+0x214/0x330
> > > >   ? process_echoes+0x60/0x60
> > > >   ib_uverbs_ioctl+0xa7/0x110 [ib_uverbs]
> > > >   __x64_sys_ioctl+0x10d/0x8e0
> > > >   ? vfs_write+0x17f/0x260
> > > >   do_syscall_64+0x3c/0x80
> > > >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> > > > 
> > > > Fixes: a639e66703ee ("RDMA/mlx5: Zero out ODP related items in the mlx5_ib_mr")
> > > Can you explain why this is crashing?
> > > 
> > > reg_create isn't used on the ODP implicit children path.
> > > 
> > > Jason
> > It is not implicit ODP flow, therefore, mr->implicit_children shouldn't be
> > set.
> 
> It should always be initialized. That seems to be the bug here, add the
> missing xa_init as well as delete the extra desc_size set:

I would expect such change in mlx5_ib_init_odp_mr().

> 
> diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
> index b4d2322e9ca564..46626e0fe08905 100644
> --- a/drivers/infiniband/hw/mlx5/mr.c
> +++ b/drivers/infiniband/hw/mlx5/mr.c
> @@ -1525,6 +1525,7 @@ static struct ib_mr *create_user_odp_mr(struct ib_pd *pd, u64 start, u64 length,
>                 ib_umem_release(&odp->umem);
>                 return ERR_CAST(mr);
>         }
> +       xa_init(&mr->implicit_children);
>  
>         odp->private = mr;
>         err = mlx5r_store_odp_mkey(dev, &mr->mmkey);
> 
> Jason