Re: [PATCH RFC v2 00/19] fuse: fuse-over-io-uring

[Bernd Schubert <bschubert@ddn.com>]

On 8/30/24 15:12, Jens Axboe wrote:
> On 8/29/24 4:32 PM, Bernd Schubert wrote:
>> Wanted to send out a new series today, 
>>
>> https://github.com/bsbernd/linux/tree/fuse-uring-for-6.10-rfc3-without-mmap
>>
>> but then just noticed a tear down issue.
>>
>>  1525.905504] KASAN: null-ptr-deref in range [0x00000000000001a0-0x00000000000001a7]
>> [ 1525.910431] CPU: 15 PID: 183 Comm: kworker/15:1 Tainted: G           O       6.10.0+ #48
>> [ 1525.916449] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>> [ 1525.922470] Workqueue: events io_fallback_req_func
>> [ 1525.925840] RIP: 0010:__lock_acquire+0x74/0x7b80
>> [ 1525.929010] Code: 89 bc 24 80 00 00 00 0f 85 1c 5f 00 00 83 3d 6e 80 b0 02 00 0f 84 1d 12 00 00 83 3d 65 c7 67 02 00 74 27 48 89 f8 48 c1 e8 03 <42> 80 3c 30 00 74 0d e8 50 44 42 00 48 8b bc 24 80 00 00 00 48 c7
>> [ 1525.942211] RSP: 0018:ffff88810b2af490 EFLAGS: 00010002
>> [ 1525.945672] RAX: 0000000000000034 RBX: 0000000000000000 RCX: 0000000000000001
>> [ 1525.950421] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000001a0
>> [ 1525.955200] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
>> [ 1525.959979] R10: dffffc0000000000 R11: fffffbfff07b1cbe R12: 0000000000000000
>> [ 1525.964252] R13: 0000000000000001 R14: dffffc0000000000 R15: 0000000000000001
>> [ 1525.968225] FS:  0000000000000000(0000) GS:ffff88875b200000(0000) knlGS:0000000000000000
>> [ 1525.973932] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 1525.976694] CR2: 00005555b6a381f0 CR3: 000000012f5f1000 CR4: 00000000000006f0
>> [ 1525.980030] Call Trace:
>> [ 1525.981371]  <TASK>
>> [ 1525.982567]  ? __die_body+0x66/0xb0
>> [ 1525.984376]  ? die_addr+0xc1/0x100
>> [ 1525.986111]  ? exc_general_protection+0x1c6/0x330
>> [ 1525.988401]  ? asm_exc_general_protection+0x22/0x30
>> [ 1525.990864]  ? __lock_acquire+0x74/0x7b80
>> [ 1525.992901]  ? mark_lock+0x9f/0x360
>> [ 1525.994635]  ? __lock_acquire+0x1420/0x7b80
>> [ 1525.996629]  ? attach_entity_load_avg+0x47d/0x550
>> [ 1525.998765]  ? hlock_conflict+0x5a/0x1f0
>> [ 1526.000515]  ? __bfs+0x2dc/0x5a0
>> [ 1526.001993]  lock_acquire+0x1fb/0x3d0
>> [ 1526.004727]  ? gup_fast_fallback+0x13f/0x1d80
>> [ 1526.006586]  ? gup_fast_fallback+0x13f/0x1d80
>> [ 1526.008412]  gup_fast_fallback+0x158/0x1d80
>> [ 1526.010170]  ? gup_fast_fallback+0x13f/0x1d80
>> [ 1526.011999]  ? __lock_acquire+0x2b07/0x7b80
>> [ 1526.013793]  __iov_iter_get_pages_alloc+0x36e/0x980
>> [ 1526.015876]  ? do_raw_spin_unlock+0x5a/0x8a0
>> [ 1526.017734]  iov_iter_get_pages2+0x56/0x70
>> [ 1526.019491]  fuse_copy_fill+0x48e/0x980 [fuse]
>> [ 1526.021400]  fuse_copy_args+0x174/0x6a0 [fuse]
>> [ 1526.023199]  fuse_uring_prepare_send+0x319/0x6c0 [fuse]
>> [ 1526.025178]  fuse_uring_send_req_in_task+0x42/0x100 [fuse]
>> [ 1526.027163]  io_fallback_req_func+0xb4/0x170
>> [ 1526.028737]  ? process_scheduled_works+0x75b/0x1160
>> [ 1526.030445]  process_scheduled_works+0x85c/0x1160
>> [ 1526.032073]  worker_thread+0x8ba/0xce0
>> [ 1526.033388]  kthread+0x23e/0x2b0
>> [ 1526.035404]  ? pr_cont_work_flush+0x290/0x290
>> [ 1526.036958]  ? kthread_blkcg+0xa0/0xa0
>> [ 1526.038321]  ret_from_fork+0x30/0x60
>> [ 1526.039600]  ? kthread_blkcg+0xa0/0xa0
>> [ 1526.040942]  ret_from_fork_asm+0x11/0x20
>> [ 1526.042353]  </TASK>
>>
>>
>> We probably need to call iov_iter_get_pages2() immediately
>> on submitting the buffer from fuse server and not only when needed.
>> I had planned to do that as optimization later on, I think
>> it is also needed to avoid io_uring_cmd_complete_in_task().
> 
> I think you do, but it's not really what's wrong here - fallback work is
> being invoked as the ring is being torn down, either directly or because
> the task is exiting. Your task_work should check if this is the case,
> and just do -ECANCELED for this case rather than attempt to execute the
> work. Most task_work doesn't do much outside of post a completion, but
> yours seems complex in that attempts to map pages as well, for example.
> In any case, regardless of whether you move the gup to the actual issue
> side of things (which I think you should), then you'd want something
> ala:
> 
> if (req->task != current)
> 	don't issue, -ECANCELED
> 
> in your task_work.

Thanks a lot for your help Jens! I'm a bit confused, doesn't this belong 
into __io_uring_cmd_do_in_task then? Because my task_work_cb function 
(passed to io_uring_cmd_complete_in_task) doesn't even have the request.

I'm going to test this in a bit

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 21ac5fb2d5f0..c06b9fcff48f 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -120,6 +120,11 @@ static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts)
 {
        struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
 
+       if (req->task != current) {
+               /* don't issue, -ECANCELED */
+               return;
+       }
+
        /* task_work executor checks the deffered list completion */
        ioucmd->task_work_cb(ioucmd, IO_URING_F_COMPLETE_DEFER);
 }



> 
>> The part I don't like here is that with mmap we had a complex
>> initialization - but then either it worked or did not. No exceptions
>> at IO time. And run time was just a copy into the buffer. 
>> Without mmap initialization is much simpler, but now complexity shifts
>> to IO time.
> 
> I'll take a look at your code. But I'd say just fix the missing check
> above and send out what you have, it's much easier to iterate on the
> list rather than poking at patches in some git branch somewhere.
> 

I'm almost through updating it, will send something out definitely today.
I will just keep the last patch that pins user buffer pages on top of the series 
- will avoid all the rebasing.


Thanks,
Bernd