linux-kernel - Re: [PATCH] IB/iser: Protect tasks cleanup in case iser connection was stopped

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Date:   Wed, 5 Jul 2023 10:54:03 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     lihongweizz <lihongweizz@...pur.com>
Cc:     sagi@...mberg.me, mgurtovoy@...dia.com, jgg@...pe.ca,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/iser: Protect tasks cleanup in case iser connection
 was stopped

On Tue, Jul 04, 2023 at 08:51:44AM +0800, lihongweizz wrote:
> From: Rock Li <lihongweizz@...pur.com>
> 
> We met a crash issue as below:
> ...
>  #7 [ff61b991f6f63d10] page_fault at ffffffffab80111e
>     [exception RIP: iscsi_iser_cleanup_task+13]
>     RIP: ffffffffc046c04d RSP: ff61b991f6f63dc0 RFLAGS: 00010246
>     RAX: 0000000000000000 RBX: ff4bd0aalf7a5610 RCX: ff61b991f6f63dc8
>     RDX: ff61b991f6f63d68 RSI: ff61b991f6f63d58 RDI: ff4bd0aalf6cdc00
>     RBP: 0000000000000005 R8: 0000000000000073 R9: 0000000000000005
>     R10: 0000000000000000 R11: 00000ccde3e0f5c0 R12: ff4bd08c0e0631f8
>     R13: ff4bd0a95ffd3c78 R14: ff4bd0a95ffd3c78 R15: ff4bd0aalf6cdc00
>     ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>  #8 [ff616991f6f63dc0] __iscsi_put_task at ffffffffc0bd3652 [libiscsi]
>  #9 [ff61b991f6f63e00] iscsi_put_task at ffffffffc0bd36e9 [libiscsi]
> ...
> 
> After analysing the vmcore, we find that the iser connection was already
> stopped before abort handler running. The iser_conn is already unbindded
> and released. So we add iser connection validation check inside cleanup
> task to fix this corner case.
> 
> Signed-off-by: Rock Li <lihongweizz@...pur.com>
> ---
>  drivers/infiniband/ulp/iser/iscsi_iser.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c b/drivers/infiniband/ulp/iser/iscsi_iser.c
> index bb9aaff92ca3..35dfbf41fc40 100644
> --- a/drivers/infiniband/ulp/iser/iscsi_iser.c
> +++ b/drivers/infiniband/ulp/iser/iscsi_iser.c
> @@ -366,7 +366,12 @@ static void iscsi_iser_cleanup_task(struct iscsi_task *task)
>  	struct iscsi_iser_task *iser_task = task->dd_data;
>  	struct iser_tx_desc *tx_desc = &iser_task->desc;
>  	struct iser_conn *iser_conn = task->conn->dd_data;
> -	struct iser_device *device = iser_conn->ib_conn.device;
> +	struct iser_device *device;
> +
> +	/* stop connection might happens before iser cleanup work */
> +	if (!iser_conn)
> +		return;

And what prevents from iser_conn being not valid here?
For example, in the flow:
1. Start iscsi_iser_cleanup_task
2. Get valid task->conn->dd_data
3. Pass this if (..) check
4. Context switch and release connection
5. iser_conn now points to released memory.

Thanks

> +	device = iser_conn->ib_conn.device;
>  
>  	/* DEVICE_REMOVAL event might have already released the device */
>  	if (!device)
> -- 
> 2.27.0
>