Re: [PATCH] cxgb3i: ref count cdev access to prevent modification while in use (v2)

[James Bottomley <jbottomley@parallels.com>]

On Thu, 2011-08-11 at 10:55 -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
> 
> Change notes:
> 
> v2) Resent because of some build warnings with the first version on request of
> JBottomley
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> CC: Divy Le Ray <divy@chelsio.com>
> CC: Steve Wise <swise@chelsio.com>
> CC: Karen Xie <kxie@chelsio.com>
> CC: Mike Christie <michaelc@cs.wisc.edu>
> CC: "James E.J. Bottomley" <JBottomley@parallels.com>
> CC: stable@vger.kernel.org
> ---
>  drivers/scsi/cxgbi/cxgb3i/cxgb3i.c |    8 +++++++-
>  drivers/scsi/cxgbi/libcxgbi.c      |   11 ++++++++++-
>  drivers/scsi/cxgbi/libcxgbi.h      |    3 +++
>  3 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/cxgbi/cxgb3i/cxgb3i.c b/drivers/scsi/cxgbi/cxgb3i/cxgb3i.c
> index bd22041..d04e167 100644
> --- a/drivers/scsi/cxgbi/cxgb3i/cxgb3i.c
> +++ b/drivers/scsi/cxgbi/cxgb3i/cxgb3i.c
> @@ -1303,9 +1303,13 @@ static void cxgb3i_dev_close(struct t3cdev *t3dev)
>  
>  	if (!cdev || cdev->flags & CXGBI_FLAG_ADAPTER_RESET) {
>  		pr_info("0x%p close, f 0x%x.\n", cdev, cdev ? cdev->flags : 0);
> +		if (cdev)
> +			cdev_put(cdev);
> +		while (cdev && atomic_read(&cdev->use_count) != 0)
> +			msleep(1);
>  		return;
>  	}
> -
> +	cdev_put(cdev);
>  	cxgbi_device_unregister(cdev);
>  }
>  
> @@ -1320,6 +1324,7 @@ static void cxgb3i_dev_open(struct t3cdev *t3dev)
>  	int i, err;
>  
>  	if (cdev) {
> +		cdev_put(cdev);
>  		pr_info("0x%p, updating.\n", cdev);
>  		return;
>  	}
> @@ -1392,6 +1397,7 @@ static void cxgb3i_dev_event_handler(struct t3cdev *t3dev, u32 event, u32 port)
>  		cdev->flags &= ~CXGBI_FLAG_ADAPTER_RESET;
>  		break;
>  	}
> +	cdev_put(cdev);
>  }
>  
>  /**
> diff --git a/drivers/scsi/cxgbi/libcxgbi.c b/drivers/scsi/cxgbi/libcxgbi.c
> index 77ac217..0890728 100644
> --- a/drivers/scsi/cxgbi/libcxgbi.c
> +++ b/drivers/scsi/cxgbi/libcxgbi.c
> @@ -181,6 +181,9 @@ struct cxgbi_device *cxgbi_device_find_by_lldev(void *lldev)
>  	mutex_lock(&cdev_mutex);
>  	list_for_each_entry_safe(cdev, tmp, &cdev_list, list_head) {
>  		if (cdev->lldev == lldev) {
> +			if (cdev->flags & CXGBI_FLAG_ADAPTER_RESET)
> +				continue;
> +			cdev_hold(cdev);
>  			mutex_unlock(&cdev_mutex);
>  			return cdev;
>  		}
> @@ -210,7 +213,10 @@ static struct cxgbi_device *cxgbi_device_find_by_netdev(struct net_device *ndev,
>  	list_for_each_entry_safe(cdev, tmp, &cdev_list, list_head) {
>  		for (i = 0; i < cdev->nports; i++) {
>  			if (ndev == cdev->ports[i]) {
> +				if (cdev->flags & CXGBI_FLAG_ADAPTER_RESET)
> +					continue;
>  				cdev->hbas[i]->vdev = vdev;
> +				cdev_hold(cdev);
>  				mutex_unlock(&cdev_mutex);
>  				if (port)
>  					*port = i;
> @@ -469,7 +475,7 @@ static struct cxgbi_sock *cxgbi_check_route(struct sockaddr *dst_addr)
>  	struct sockaddr_in *daddr = (struct sockaddr_in *)dst_addr;
>  	struct dst_entry *dst;
>  	struct net_device *ndev;
> -	struct cxgbi_device *cdev;
> +	struct cxgbi_device *cdev = NULL;
>  	struct rtable *rt = NULL;
>  	struct flowi4 fl4;
>  	struct cxgbi_sock *csk = NULL;
> @@ -542,6 +548,8 @@ rel_rt:
>  	if (csk)
>  		cxgbi_sock_closed(csk);
>  err_out:
> +	if (cdev)
> +		cdev_put(cdev);
>  	return ERR_PTR(err);
>  }
>  
> @@ -2491,6 +2499,7 @@ struct iscsi_endpoint *cxgbi_ep_connect(struct Scsi_Host *shost,
>  	return ep;
>  
>  release_conn:
> +	cdev_put(csk->cdev);
>  	cxgbi_sock_put(csk);
>  	cxgbi_sock_closed(csk);
>  err_out:
> diff --git a/drivers/scsi/cxgbi/libcxgbi.h b/drivers/scsi/cxgbi/libcxgbi.h
> index 9267844..aad1749 100644
> --- a/drivers/scsi/cxgbi/libcxgbi.h
> +++ b/drivers/scsi/cxgbi/libcxgbi.h
> @@ -514,6 +514,7 @@ struct cxgbi_device {
>  	unsigned int flags;
>  	struct net_device **ports;
>  	void *lldev;
> +	atomic_t use_count;
>  	struct cxgbi_hba **hbas;
>  	const unsigned short *mtus;
>  	unsigned char nmtus;
> @@ -557,6 +558,8 @@ struct cxgbi_device {
>  	void *dd_data;
>  };
>  #define cxgbi_cdev_priv(cdev)	((cdev)->dd_data)
> +#define cdev_hold(x) do {atomic_inc(&x->use_count);} while(0)
> +#define cdev_put(x) do {atomic_dec(&x->use_count);} while(0)

OK, so now I read the patch, this is obviously wrong because you're hand
rolling refcounting with atomics.

Surely what cxgbi_device wants is an embedded kref which calls
cxgbi_device_destroy() on final put?

James