Re: [PATCH v7 07/24] IB/umem: use get_user_pages_fast() to pin DMA pages

John Hubbard
2019-11-25T00:05:26Z

On 11/24/19 2:07 AM, Leon Romanovsky wrote:
> On Thu, Nov 21, 2019 at 10:36:43AM -0400, Jason Gunthorpe wrote:
>> On Thu, Nov 21, 2019 at 12:07:46AM -0800, Christoph Hellwig wrote:
>>> On Wed, Nov 20, 2019 at 11:13:37PM -0800, John Hubbard wrote:
>>>> And get rid of the mmap_sem calls, as part of that. Note
>>>> that get_user_pages_fast() will, if necessary, fall back to
>>>> __gup_longterm_unlocked(), which takes the mmap_sem as needed.
>>>>
>>>> Reviewed-by: Jan Kara <jack@suse.cz>
>>>> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
>>>> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>>>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>>>
>>> Looks fine,
>>>
>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>>
>>> Jason, can you queue this up for 5.5 to reduce this patch stack a bit?
>>
>> Yes, I said I'd do this in an earlier revision. Now that it is clear this
>> won't go through Andrew's tree, applied to rdma for-next
>
> Jason,
>
> This patch broke RDMA completely.
> Change from get_user_pages() to get_user_pages_fast() causes to endless
> amount of splats due to combination of the following code:
>
> 189 struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
> 190 size_t size, int access)
> ...
> 263 if (!umem->writable)
> 264 gup_flags |= FOLL_FORCE;
> 265
>
> and
>
> 2398 int get_user_pages_fast(unsigned long start, int nr_pages,
> 2399 unsigned int gup_flags, struct page **pages)
> 2400 {
> 2401 unsigned long addr, len, end;
> 2402 int nr = 0, ret = 0;
> 2403
> 2404 if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
> 2405 return -EINVAL;
>

Hi Leon,

I looked into this, and I believe that the problem is in gup.c. There appears to
have been an oversight, in commit 817be129e6f2 ("mm: validate get_user_pages_fast
flags"), in filtering out FOLL_FORCE. There is nothing in the _fast() implementation
that requires that we avoid writing to the pages.

So I intend, to post a two-patch series that includes this fix, first, but maybe this
means that it should go in via -mm. I'm not sure what's the best tree.

diff --git a/mm/gup.c b/mm/gup.c
index 8f236a335ae9..745b4036cdfd 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2401,7 +2401,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned long addr, len, end;
int nr = 0, ret = 0;

- if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
+ if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
+ FOLL_FORCE)))
return -EINVAL;

start = untagged_addr(start) & PAGE_MASK;

thanks,
--
John Hubbard
NVIDIA

>
> [ 72.623266] ------------[ cut here ]------------
> [ 72.624143] WARNING: CPU: 1 PID: 2557 at mm/gup.c:2404 get_user_pages_fast+0x115/0x180
> [ 72.625426] Modules linked in: xt_MASQUERADE iptable_nat nf_nat
> br_netfilter overlay ib_srp scsi_transport_srp rpcrdma rdma_ucm
> ib_iser libiscsi scsi_transport_iscsi rdma_cm ib_umad iw_cm ib_ipoib
> ib_cm mlx5_ib ib_uverbs ib_core mlx5_core mlxfw ptp pps_core
> [ 72.629024] CPU: 1 PID: 2557 Comm: python3 Not tainted 5.4.0-rc5-J6120-Geeb831ec5b80 #1
> [ 72.630435] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
> [ 72.631973] RIP: 0010:get_user_pages_fast+0x115/0x180
> [ 72.632873] Code: 8d 0c 10 85 c0 89 d0 0f 49 c1 eb 97 fa 4c 8d
> 44 24 0c 4c 89 e9 44 89 e2 48 89 df e8 25 dd ff ff fb 8b 44 24 0c
> e9 75 ff ff ff <0f> 0b b8 ea ff ff ff e9 6d ff ff ff 65 4c 8b 2c
> 25 00 5d 01 00 49
> [ 72.635967] RSP: 0018:ffffc90000edf930 EFLAGS: 00010202
> [ 72.636896] RAX: 0000000000000000 RBX: 00007f931c392000 RCX: ffff8883f4909000
> [ 72.638117] RDX: 0000000000010011 RSI: 0000000000000001 RDI: 00007f931c392000
> [ 72.639353] RBP: 00007f931c392000 R08: 0000000000000020 R09: ffff8883f4909000
> [ 72.640602] R10: 0000000000000000 R11: ffff8884068d6760 R12: ffff888409e45ba0
> [ 72.641858] R13: ffff8884068d6760 R14: 0000160000000000 R15: ffff8883f4909000
> [ 72.643115] FS: 00007f9323754700(0000) GS:ffff88842fa80000(0000) knlGS:0000000000000000
> [ 72.644586] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 72.645628] CR2: 00007f931c3ca000 CR3: 00000003f83d6006 CR4: 00000000007606a0
> [ 72.646875] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 72.648120] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 72.649374] PKRU: 55555554
> [ 72.649935] Call Trace:
> [ 72.650477] ib_umem_get+0x298/0x550 [ib_uverbs]
> [ 72.651347] mlx5_ib_db_map_user+0xad/0x130 [mlx5_ib]
> [ 72.652279] mlx5_ib_create_cq+0x1e8/0xaa0 [mlx5_ib]
> [ 72.653207] create_cq+0x1c8/0x2d0 [ib_uverbs]
> [ 72.654050] ib_uverbs_create_cq+0x70/0xa0 [ib_uverbs]
> [ 72.654988] ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0xc2/0xf0 [ib_uverbs]
> [ 72.656331] ib_uverbs_cmd_verbs.isra.6+0x5be/0xbe0 [ib_uverbs]
> [ 72.657398] ? uverbs_disassociate_api+0xd0/0xd0 [ib_uverbs]
> [ 72.658423] ? kvm_clock_get_cycles+0xd/0x10
> [ 72.659229] ? kmem_cache_alloc+0x176/0x1c0
> [ 72.660025] ? filemap_map_pages+0x18c/0x350
> [ 72.660838] ib_uverbs_ioctl+0xc0/0x120 [ib_uverbs]
> [ 72.661756] do_vfs_ioctl+0xa1/0x610
> [ 72.662458] ksys_ioctl+0x70/0x80
> [ 72.663119] __x64_sys_ioctl+0x16/0x20
> [ 72.663850] do_syscall_64+0x42/0x110
> [ 72.664562] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 72.665492] RIP: 0033:0x7f9332958267
> [ 72.666185] Code: b3 66 90 48
> 8b 05 19 3c 2c 00 64 c7 00 26 00
> 00 00 48 c7 c0 ff ff ff ff c3 66
> 2e 0f 1f 84 00 00 00 00 00 b8 10
> 00 00 00 0f 05 <48> 3d 01 f0 ff
> ff 73 01 c3 48 8b 0d e9 3b 2c 00
> f7 d8 64 89 01 48
> [ 72.669347] RSP: 002b:00007f9323751928 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [ 72.670706] RAX: ffffffffffffffda RBX: 00007f93237519b8 RCX: 00007f9332958267
> [ 72.671937] RDX: 00007f93237519a0 RSI: 00000000c0181b01 RDI: 0000000000000008
> [ 72.673176] RBP: 00007f9323751980 R08: 0000000000000005 R09: 00007f931c3ffef0
> [ 72.674415] R10: 0000000000001000 R11: 0000000000000246 R12: 00007f931c400030
> [ 72.675653] R13: 00007f9323751980 R14: 00007f9323751ea8 R15: 00000000000000ff
> [ 72.676885] ---[ end trace 033465440517865c ]---
>
>>
>> Thanks,
>> Jason
>>