netdev - Re: [PATCH] cxgb3i: ref count cdev access to prevent modification while in use

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Message-ID: <20110801111824.GB23131@hmsreliant.think-freely.org>
Date:	Mon, 1 Aug 2011 07:18:24 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	netdev@...r.kernel.org
Cc:	Divy Le Ray <divy@...lsio.com>, Steve Wise <swise@...lsio.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] cxgb3i: ref count cdev access to prevent modification
 while in use

On Mon, Jul 25, 2011 at 03:56:57PM -0400, Neil Horman wrote:
> This oops was reported recently:
> d:mon> e
> cpu 0xd: Vector: 300 (Data Access) at [c0000000fd4c7120]
>     pc: d00000000076f194: .t3_l2t_get+0x44/0x524 [cxgb3]
>     lr: d000000000b02108: .init_act_open+0x150/0x3d4 [cxgb3i]
>     sp: c0000000fd4c73a0
>    msr: 8000000000009032
>    dar: 0
>  dsisr: 40000000
>   current = 0xc0000000fd640d40
>   paca    = 0xc00000000054ff80
>     pid   = 5085, comm = iscsid
> d:mon> t
> [c0000000fd4c7450] d000000000b02108 .init_act_open+0x150/0x3d4 [cxgb3i]
> [c0000000fd4c7500] d000000000e45378 .cxgbi_ep_connect+0x784/0x8e8 [libcxgbi]
> [c0000000fd4c7650] d000000000db33f0 .iscsi_if_rx+0x71c/0xb18
> [scsi_transport_iscsi2]
> [c0000000fd4c7740] c000000000370c9c .netlink_data_ready+0x40/0xa4
> [c0000000fd4c77c0] c00000000036f010 .netlink_sendskb+0x4c/0x9c
> [c0000000fd4c7850] c000000000370c18 .netlink_sendmsg+0x358/0x39c
> [c0000000fd4c7950] c00000000033be24 .sock_sendmsg+0x114/0x1b8
> [c0000000fd4c7b50] c00000000033d208 .sys_sendmsg+0x218/0x2ac
> [c0000000fd4c7d70] c00000000033f55c .sys_socketcall+0x228/0x27c
> [c0000000fd4c7e30] c0000000000086a4 syscall_exit+0x0/0x40
> --- Exception: c01 (System Call) at 00000080da560cfc
> 
> The root cause was an EEH error, which sent us down the offload_close path in
> the cxgb3 driver, which in turn sets cdev->lldev to NULL, without regard for
> upper layer driver (like the cxgbi drivers) which might have execution contexts
> in the middle of its use. The result is the oops above, when t3_l2t_get attempts
> to dereference cdev->lldev right after the EEH error handler sets it to NULL.
> 
> The fix is to reference count the cdev structure.  When an EEH error occurs, the
> shutdown path:
> t3_adapter_error->offload_close->cxgb3i_remove_clients->cxgb3i_dev_close
> will now block until such time as the cdev pointer has a use count of zero.
> This coupled with the fact that lookups will now skip finding any registered
> cdev's in cxgbi_device_find_by_[lldev|netdev] with the CXGBI_FLAG_ADAPTER_RESET
> bit set ensures that on an EEH, the setting of lldev to NULL in offload_close
> will only happen after there are no longer any active users of the data
> structure.
> 
> This has been tested by the reporter and shown to fix the reproted oops
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Divy Le Ray <divy@...lsio.com>
> CC: Steve Wise <swise@...lsio.com>
> CC: "David S. Miller" <davem@...emloft.net>
Divy, Steve, I think Dave is waiting for an ACK from one of you to, since you're
the listed maintainers.
Neil
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