RE: [PATCH 2/2 V3 net] net: mana: Fix MANA VF unload when host is unresponsive

[Haiyang Zhang]

> -----Original Message-----
> From: Praveen Kumar <kumarpraveen@xxxxxxxxxxxxxxxxxxx>
> Sent: Monday, June 26, 2023 10:13 AM
> To: souradeep chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>; KY Srinivasan
> <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>;
> wei.liu@xxxxxxxxxx; Dexuan Cui <decui@xxxxxxxxxxxxx>;
> davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; Long Li <longli@xxxxxxxxxxxxx>; Ajay Sharma
> <sharmaajay@xxxxxxxxxxxxx>; leon@xxxxxxxxxx; cai.huoqing@xxxxxxxxx;
> ssengar@xxxxxxxxxxxxxxxxxxx; vkuznets@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; linux-
> hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-rdma@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx; Souradeep Chakrabarti
> <schakrabarti@xxxxxxxxxxxxx>
> Subject: Re: [PATCH 2/2 V3 net] net: mana: Fix MANA VF unload when host is
> unresponsive
> 
> On 6/26/2023 2:50 PM, souradeep chakrabarti wrote:
> > From: Souradeep Chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>
> >
> > This is the second part of the fix.
> >
> > Also this patch adds a new attribute in mana_context, which gets set when
> > mana_hwc_send_request() hits a timeout because of host unresponsiveness.
> > This flag then helps to avoid the timeouts in successive calls.
> >
> > Fixes: ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f (net: mana: Add a
> driver for
> > Microsoft Azure Network Adapter)
> > Signed-off-by: Souradeep Chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>
> > ---
> > V2 -> V3:
> > * Removed the initialization of vf_unload_timeout
> > * Splitted the patch in two.
> > * Fixed extra space from the commit message.
> > ---
> >  drivers/net/ethernet/microsoft/mana/gdma_main.c  |  4 +++-
> >  drivers/net/ethernet/microsoft/mana/hw_channel.c | 12 +++++++++++-
> >  include/net/mana/mana.h                          |  2 ++
> >  3 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > index 8f3f78b68592..6411f01be0d9 100644
> > --- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > @@ -946,10 +946,12 @@ int mana_gd_deregister_device(struct gdma_dev
> *gd)
> >  	struct gdma_context *gc = gd->gdma_context;
> >  	struct gdma_general_resp resp = {};
> >  	struct gdma_general_req req = {};
> > +	struct mana_context *ac;
> >  	int err;
> >
> >  	if (gd->pdid == INVALID_PDID)
> >  		return -EINVAL;
> > +	ac = gd->driver_data;
> >
> >  	mana_gd_init_req_hdr(&req.hdr, GDMA_DEREGISTER_DEVICE,
> sizeof(req),
> >  			     sizeof(resp));
> > @@ -957,7 +959,7 @@ int mana_gd_deregister_device(struct gdma_dev *gd)
> >  	req.hdr.dev_id = gd->dev_id;
> >
> >  	err = mana_gd_send_request(gc, sizeof(req), &req, sizeof(resp), &resp);
> > -	if (err || resp.hdr.status) {
> > +	if ((err || resp.hdr.status) && !ac->vf_unload_timeout) {
> >  		dev_err(gc->dev, "Failed to deregister device: %d, 0x%x\n",
> >  			err, resp.hdr.status);
> 
> With !ac->vf_unload_timeout option, this message may not be correctly
> showing err, status. Probably you want to add explicit information during
> timeouts so that it give right information ? Or have the err, status field properly
> updated.
> 
> >  		if (!err)
> > diff --git a/drivers/net/ethernet/microsoft/mana/hw_channel.c
> b/drivers/net/ethernet/microsoft/mana/hw_channel.c
> > index 9d1507eba5b9..492cb2c6e2cb 100644
> > --- a/drivers/net/ethernet/microsoft/mana/hw_channel.c
> > +++ b/drivers/net/ethernet/microsoft/mana/hw_channel.c
> > @@ -1,8 +1,10 @@
> >  // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
> >  /* Copyright (c) 2021, Microsoft Corporation. */
> >
> > +#include "asm-generic/errno.h"
> >  #include <net/mana/gdma.h>
> >  #include <net/mana/hw_channel.h>
> > +#include <net/mana/mana.h>
> >
> >  static int mana_hwc_get_msg_index(struct hw_channel_context *hwc, u16
> *msg_id)
> >  {
> > @@ -786,12 +788,19 @@ int mana_hwc_send_request(struct
> hw_channel_context *hwc, u32 req_len,
> >  	struct hwc_wq *txq = hwc->txq;
> >  	struct gdma_req_hdr *req_msg;
> >  	struct hwc_caller_ctx *ctx;
> > +	struct mana_context *ac;
> >  	u32 dest_vrcq = 0;
> >  	u32 dest_vrq = 0;
> >  	u16 msg_id;
> >  	int err;
> >
> >  	mana_hwc_get_msg_index(hwc, &msg_id);
> > +	ac = hwc->gdma_dev->driver_data;
> 
> Is there a case where gdma_dev be invalid here ? If so, lets check the state and
> then proceed further ?

Yes, hwc->gdma_dev is assigned shortly after it's allocated - see the code below. So
it's valid.
But hwc->gdma_dev->driver_data is hwc, not "mana_context *ac". There are two 
gdma_dev in gdma_context: hwc & mana.

You can get ac from: hwc->gdma_dev->gdma_context->mana.driver_data
Or, to avoid too many pointer deference, I suggest to put the vf_unload_timeout 
into gdma_context.

int mana_hwc_create_channel(struct gdma_context *gc)
{
        hwc = kzalloc(sizeof(*hwc), GFP_KERNEL);
...
        gd->gdma_context = gc;
        gd->driver_data = hwc;
        hwc->gdma_dev = gd;
        hwc->dev = gc->dev;


Also, mana_gd_send_request/mana_hwc_send_request() is used in many places,
not just unloading.
Should you use timeout value 5 sec, and the vf_unload_timeout flag in unloading
path only, and avoid touching other code paths? Please check with hostnet team for
suggestions.

If we decide to let the vf_unload_timeout flag affect all code paths, not just 
unloading, then it should be renamed to hwc_timeout, and submit the second patch
separately.
If just use it for unloading, since mana_gd_deregister_device() is used by PF too, 
name it like: unload_hwc_timeout.

Thanks,
-Haiyang