Re: [PATCH for-rc 5/7] IB/hfi1: Close race condition on user context disable and close

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On Thu, Jan 17, 2019 at 12:41:54PM -0800, Dennis Dalessandro wrote:
> From: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
> 
> When disabling and removing a receive context, it is possible for an
> asynchronous event (i.e IRQ) to occur.  Because of this there is a
> race between cleaning up the context, and the context being used by
> the asynchronous event.
> 
> cpu 0  (context cleanup)
>     rc->ref_count-- (ref_count == 0)
>     hfi1_rcd_free()
> cpu 1  (IRQ (with rcd index))
> 	rcd_get_by_index()
> 	lock
> 	ref_count+++     <-- reference count race (WARNING)
> 	return rcd
> 	unlock
> cpu 0
>     hfi1_free_ctxtdata() <-- incorrect free location
>     lock
>     remove rcd from array
>     unlock
>     free rcd
> 
> This race will cause the following WARNING trace:
> 
> WARNING: CPU: 0 PID: 175027 at include/linux/kref.h:52 hfi1_rcd_get_by_index+0x84/0xa0 [hfi1]
> CPU: 0 PID: 175027 Comm: IMB-MPI1 Kdump: loaded Tainted: G OE ------------ 3.10.0-957.el7.x86_64 #1
> Hardware name: Intel Corporation S2600KP/S2600KP, BIOS SE5C610.86B.11.01.0076.C4.111920150602 11/19/2015
> Call Trace:
>   dump_stack+0x19/0x1b
>   __warn+0xd8/0x100
>   warn_slowpath_null+0x1d/0x20
>   hfi1_rcd_get_by_index+0x84/0xa0 [hfi1]
>   is_rcv_urgent_int+0x24/0x90 [hfi1]
>   general_interrupt+0x1b6/0x210 [hfi1]
>   __handle_irq_event_percpu+0x44/0x1c0
>   handle_irq_event_percpu+0x32/0x80
>   handle_irq_event+0x3c/0x60
>   handle_edge_irq+0x7f/0x150
>   handle_irq+0xe4/0x1a0
>   do_IRQ+0x4d/0xf0
>   common_interrupt+0x162/0x162
> 
> The race can also lead to a use after free which could be similar
> to:
> 
> general protection fault: 0000 1 SMP
> CPU: 71 PID: 177147 Comm: IMB-MPI1 Kdump: loaded Tainted: G W OE ------------ 3.10.0-957.el7.x86_64 #1
> Hardware name: Intel Corporation S2600KP/S2600KP, BIOS SE5C610.86B.11.01.0076.C4.111920150602 11/19/2015
> task: ffff9962a8098000 ti: ffff99717a508000 task.ti: ffff99717a508000 __kmalloc+0x94/0x230
> Call Trace:
>   ? hfi1_user_sdma_process_request+0x9c8/0x1250 [hfi1]
>   hfi1_user_sdma_process_request+0x9c8/0x1250 [hfi1]
>   hfi1_aio_write+0xba/0x110 [hfi1]
>   do_sync_readv_writev+0x7b/0xd0
>   do_readv_writev+0xce/0x260
>   ? handle_mm_fault+0x39d/0x9b0
>   ? pick_next_task_fair+0x5f/0x1b0
>   ? sched_clock_cpu+0x85/0xc0
>   ? __schedule+0x13a/0x890
>   vfs_writev+0x35/0x60
>   SyS_writev+0x7f/0x110
>   system_call_fastpath+0x22/0x27
> 
> Introduce a context enable flag to indicate if the context is enabled.
> 
> Reorder context cleanup to ensure context removal before cleanup
> occurs correctly.
> 
> Cc: stable@xxxxxxxxxxxxxxx # v4.14.0+
> Fixes: f683c80ca68e ("IB/hfi1: Resolve kernel panics by reference counting receive contexts")
> Reviewed-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
> Signed-off-by: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
> Signed-off-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
>  drivers/infiniband/hw/hfi1/file_ops.c |    2 ++
>  drivers/infiniband/hw/hfi1/hfi.h      |    3 ++-
>  drivers/infiniband/hw/hfi1/init.c     |    8 +++++---
>  3 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/hfi1/file_ops.c b/drivers/infiniband/hw/hfi1/file_ops.c
> index c22ebc7..0ba0cf5 100644
> +++ b/drivers/infiniband/hw/hfi1/file_ops.c
> @@ -671,6 +671,8 @@ static int hfi1_file_close(struct inode *inode, struct file *fp)
>  	}
>  	spin_unlock_irqrestore(&dd->uctxt_lock, flags);
>  
> +	uctxt->del_pend = 1;

Not going to get good results if you update shared data outside the
lock that is reading it..

> @@ -326,7 +325,10 @@ struct hfi1_ctxtdata *hfi1_rcd_get_by_index(struct hfi1_devdata *dd, u16 ctxt)
>  	spin_lock_irqsave(&dd->uctxt_lock, flags);
>  	if (dd->rcd[ctxt]) {
>  		rcd = dd->rcd[ctxt];
> -		hfi1_rcd_get(rcd);
> +		if (rcd->del_pend)
> +			rcd = NULL;
> +		else
> +			hfi1_rcd_get(rcd);

This probably wants to be kref_get_not_zero() - why add a confusing
del_pend?

Jason



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