linux-kernel - Re: [PATCH v4 21/28] cxl/extent: Process DCD events and realize region extents

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Message-ID: <6706de3530f5c_40429294b8@iweiny-mobl.notmuch>
Date: Wed, 9 Oct 2024 14:49:09 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: "Li, Ming4" <ming4.li@...el.com>, <ira.weiny@...el.com>, Dave Jiang
	<dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, Jonathan Cameron
	<Jonathan.Cameron@...wei.com>, Navneet Singh <navneet.singh@...el.com>,
	Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>
CC: Dan Williams <dan.j.williams@...el.com>, Davidlohr Bueso
	<dave@...olabs.net>, Alison Schofield <alison.schofield@...el.com>, "Vishal
 Verma" <vishal.l.verma@...el.com>, <linux-btrfs@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 21/28] cxl/extent: Process DCD events and realize
 region extents

Li, Ming4 wrote:
> On 10/8/2024 7:16 AM, ira.weiny@...el.com wrote:
> > From: Navneet Singh <navneet.singh@...el.com>
> >

[snip]

> >
> > Signed-off-by: Navneet Singh <navneet.singh@...el.com>
> > Co-developed-by: Ira Weiny <ira.weiny@...el.com>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> >
> Hi Ira,
> 
> I guess you missed my comments for V3, I comment it again for this patch.

Apologies.  Yes I totally missed your reply.  :-(

> 
> > +static bool extents_contain(struct cxl_dax_region *cxlr_dax,
> > +			    struct cxl_endpoint_decoder *cxled,
> > +			    struct range *new_range)
> > +{
> > +	struct device *extent_device;
> > +	struct match_data md = {
> > +		.cxled = cxled,
> > +		.new_range = new_range,
> > +	};
> > +
> > +	extent_device = device_find_child(&cxlr_dax->dev, &md, match_contains);
> > +	if (!extent_device)
> > +		return false;
> > +
> > +	put_device(extent_device);
> could use __free(put_device) to drop this 'put_device(extent_device)'

Yep.

> > +	return true;
> > +}
> [...]
> > +static bool extents_overlap(struct cxl_dax_region *cxlr_dax,
> > +			    struct cxl_endpoint_decoder *cxled,
> > +			    struct range *new_range)
> > +{
> > +	struct device *extent_device;
> > +	struct match_data md = {
> > +		.cxled = cxled,
> > +		.new_range = new_range,
> > +	};
> > +
> > +	extent_device = device_find_child(&cxlr_dax->dev, &md, match_overlaps);
> > +	if (!extent_device)
> > +		return false;
> > +
> > +	put_device(extent_device);
> Same as above.

Done.

> > +	return true;
> > +}
> > +
> [...]
> > +static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
> > +				struct xarray *extent_array, int cnt)
> > +{
> > +	struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
> > +	struct cxl_mbox_dc_response *p;
> > +	struct cxl_mbox_cmd mbox_cmd;
> > +	struct cxl_extent *extent;
> > +	unsigned long index;
> > +	u32 pl_index;
> > +	int rc;
> > +
> > +	size_t pl_size = struct_size(p, extent_list, cnt);
> > +	u32 max_extents = cnt;
> > +
> > +	/* May have to use more bit on response. */
> > +	if (pl_size > cxl_mbox->payload_size) {
> > +		max_extents = (cxl_mbox->payload_size - sizeof(*p)) /
> > +			      sizeof(struct updated_extent_list);
> > +		pl_size = struct_size(p, extent_list, max_extents);
> > +	}
> > +
> > +	struct cxl_mbox_dc_response *response __free(kfree) =
> > +						kzalloc(pl_size, GFP_KERNEL);
> > +	if (!response)
> > +		return -ENOMEM;
> > +
> > +	pl_index = 0;
> > +	xa_for_each(extent_array, index, extent) {
> > +
> > +		response->extent_list[pl_index].dpa_start = extent->start_dpa;
> > +		response->extent_list[pl_index].length = extent->length;
> > +		pl_index++;
> > +		response->extent_list_size = cpu_to_le32(pl_index);
> > +
> > +		if (pl_index == max_extents) {
> > +			mbox_cmd = (struct cxl_mbox_cmd) {
> > +				.opcode = opcode,
> > +				.size_in = struct_size(response, extent_list,
> > +						       pl_index),
> > +				.payload_in = response,
> > +			};
> > +
> > +			response->flags = 0;
> > +			if (pl_index < cnt)
> > +				response->flags &= CXL_DCD_EVENT_MORE;
> 
> It should be 'response->flags |= CXL_DCD_EVENT_MORE' here.

Ah yea.  Good catch.

> 
> Another issue is if 'cnt' is N times bigger than 'max_extents'(e,g. cnt=20, max_extents=10). all responses will be sent in this xa_for_each(), and CXL_DCD_EVENT_MORE will be set in the last response but it should not be set in these cases.
> 

Ah yes.  cnt must be decremented.  As I looked at the patch just now the

	if (cnt == 0 || pl_index)

... seemed very wrong to me.  That change masked this bug.

This should fix it:

diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index d66beec687a0..99200274dea8 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -1119,10 +1119,11 @@ static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
                        if (rc)
                                return rc;
                        pl_index = 0;
+                       cnt -= pl_index;
                }
        }
 
-       if (cnt == 0 || pl_index) {
+       if (pl_index) {
                mbox_cmd = (struct cxl_mbox_cmd) {
                        .opcode = opcode,
                        .size_in = struct_size(response, extent_list,


Thank you, and sorry again for missing your feedback.

Ira

[snip]