From: Don Dutile <ddutile@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>,
Logan Gunthorpe <logang@deltatee.com>,
linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
linux-mm@kvack.org, iommu@lists.linux-foundation.org
Cc: "Stephen Bates" <sbates@raithlin.com>,
"Christoph Hellwig" <hch@lst.de>,
"Dan Williams" <dan.j.williams@intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Christian König" <christian.koenig@amd.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Jakowski Andrzej" <andrzej.jakowski@intel.com>,
"Minturn Dave B" <dave.b.minturn@intel.com>,
"Jason Ekstrand" <jason@jlekstrand.net>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Xiong Jianxin" <jianxin.xiong@intel.com>,
"Bjorn Helgaas" <helgaas@kernel.org>,
"Ira Weiny" <ira.weiny@intel.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Bjorn Helgaas" <bhelgaas@google.com>
Subject: Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance_warn()
Date: Tue, 11 May 2021 12:05:26 -0400 [thread overview]
Message-ID: <a23fdb9c-f653-e766-89e1-98550658724c@redhat.com> (raw)
In-Reply-To: <d8ac4c84-1e69-d5d6-991a-7de87c569acc@nvidia.com>
On 5/1/21 11:58 PM, John Hubbard wrote:
> On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
>> In order to call upstream_bridge_distance_warn() from a dma_map function,
>> it must not sleep. The only reason it does sleep is to allocate the seqbuf
>> to print which devices are within the ACS path.
>>
>> Switch the kmalloc call to use a passed in gfp_mask and don't print that
>> message if the buffer fails to be allocated.
>>
>> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
>> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>> ---
>> drivers/pci/p2pdma.c | 21 +++++++++++----------
>> 1 file changed, 11 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index 196382630363..bd89437faf06 100644
>> --- a/drivers/pci/p2pdma.c
>> +++ b/drivers/pci/p2pdma.c
>> @@ -267,7 +267,7 @@ static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
>> static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
>> {
>> - if (!buf)
>> + if (!buf || !buf->buffer)
>
> This is not great, sort of from an overall design point of view, even though
> it makes the rest of the patch work. See below for other ideas, that will
> avoid the need for this sort of odd point fix.
>
+1.
In fact, I didn't see how the kmalloc was changed... you refactored the code to pass-in the
GFP_KERNEL that was originally hard-coded into upstream_bridge_distance_warn();
I don't see how that avoided the kmalloc() call.
in fact, I also see you lost a failed kmalloc() check, so it seems to have taken a step back.
>> return;
>> seq_buf_printf(buf, "%s;", pci_name(pdev));
>> @@ -495,25 +495,26 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
>> static enum pci_p2pdma_map_type
>> upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
>> - int *dist)
>> + int *dist, gfp_t gfp_mask)
>> {
>> struct seq_buf acs_list;
>> bool acs_redirects;
>> int ret;
>> - seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
>> - if (!acs_list.buffer)
>> - return -ENOMEM;
>
> Another odd thing: this used to check for memory failure and just give
> up, and now it doesn't. Yes, I realize that it all still works at the
> moment, but this is quirky and we shouldn't stop here.
>
> Instead, a cleaner approach would be to push the memory allocation
> slightly higher up the call stack, out to the
> pci_p2pdma_distance_many(). So pci_p2pdma_distance_many() should make
> the kmalloc() call, and fail out if it can't get a page for the seq_buf
> buffer. Then you don't have to do all this odd stuff.
>
> Furthermore, the call sites can then decide for themselves which GFP
> flags, GFP_ATOMIC or GFP_KERNEL or whatever they want for kmalloc().
>
agree, good proposal to avoid a sleep due to kmalloc().
> A related thing: this whole exercise would go better if there were a
> preparatory patch or two that changed the return codes in this file to
> something less crazy. There are too many functions that can fail, but
> are treated as if they sort-of-mostly-would-never-fail, in the hopes of
> using the return value directly for counting and such. This is badly
> mistaken, and it leads developers to try to avoid returning -ENOMEM
> (which is what we need here).
>
> Really, these functions should all be doing "0 for success, -ERRNO for
> failure, and pass other values, including results, in the arg list".
>
WFM!
>
>> + seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, gfp_mask), PAGE_SIZE);
>> ret = upstream_bridge_distance(provider, client, dist, &acs_redirects,
>> &acs_list);
>> if (acs_redirects) {
>> pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
>> pci_name(provider));
>> - /* Drop final semicolon */
>> - acs_list.buffer[acs_list.len-1] = 0;
>> - pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
>> - acs_list.buffer);
>> +
>> + if (acs_list.buffer) {
>> + /* Drop final semicolon */
>> + acs_list.buffer[acs_list.len - 1] = 0;
>> + pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
>> + acs_list.buffer);
>> + }
>> }
>> if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED) {
>> @@ -566,7 +567,7 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
>> if (verbose)
>> ret = upstream_bridge_distance_warn(provider,
>> - pci_client, &distance);
>> + pci_client, &distance, GFP_KERNEL);
>> else
>> ret = upstream_bridge_distance(provider, pci_client,
>> &distance, NULL, NULL);
>>
>
> thanks,
next prev parent reply other threads:[~2021-05-11 16:05 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 17:01 [PATCH 00/16] Add new DMA mapping operation for P2PDMA Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance_warn() Logan Gunthorpe
2021-05-02 3:58 ` John Hubbard
2021-05-03 15:57 ` Logan Gunthorpe
2021-05-03 18:17 ` John Hubbard
2021-05-03 18:20 ` Logan Gunthorpe
2021-05-03 18:23 ` John Hubbard
2021-05-03 18:24 ` Christoph Hellwig
2021-05-11 16:05 ` Don Dutile [this message]
2021-05-11 16:12 ` Logan Gunthorpe
2021-05-11 16:23 ` Don Dutile
2021-04-08 17:01 ` [PATCH 02/16] PCI/P2PDMA: Avoid pci_get_slot() which sleeps Logan Gunthorpe
2021-05-02 5:35 ` John Hubbard
2021-05-03 16:08 ` Logan Gunthorpe
2021-05-03 18:20 ` John Hubbard
2021-05-03 18:25 ` Christoph Hellwig
2021-05-11 16:05 ` Don Dutile
2021-05-11 16:16 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-05-11 16:14 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 03/16] PCI/P2PDMA: Attempt to set map_type if it has not been set Logan Gunthorpe
2021-05-02 19:58 ` John Hubbard
2021-05-03 16:17 ` Logan Gunthorpe
2021-05-03 18:22 ` John Hubbard
2021-05-03 18:35 ` Christoph Hellwig
2021-05-03 18:46 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-04-08 17:01 ` [PATCH 04/16] PCI/P2PDMA: Refactor pci_p2pdma_map_type() to take pagmap and device Logan Gunthorpe
2021-05-02 20:41 ` John Hubbard
2021-05-03 16:30 ` Logan Gunthorpe
2021-05-03 18:31 ` John Hubbard
2021-05-03 18:56 ` Logan Gunthorpe
2021-05-03 21:54 ` John Hubbard
2021-05-03 22:57 ` Jason Gunthorpe
2021-05-03 23:40 ` John Hubbard
2021-04-08 17:01 ` [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma() Logan Gunthorpe
2021-04-27 19:22 ` Jason Gunthorpe
2021-04-27 22:49 ` Logan Gunthorpe
2021-04-27 19:31 ` Jason Gunthorpe
2021-04-27 22:55 ` Logan Gunthorpe
2021-04-27 23:01 ` Jason Gunthorpe
2021-05-03 18:28 ` Christoph Hellwig
2021-05-03 18:31 ` Logan Gunthorpe
2021-05-02 21:23 ` John Hubbard
2021-05-03 16:38 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-04-08 17:01 ` [PATCH 06/16] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL Logan Gunthorpe
2021-05-02 22:34 ` John Hubbard
2021-04-08 17:01 ` [PATCH 07/16] PCI/P2PDMA: Make pci_p2pdma_map_type() non-static Logan Gunthorpe
2021-05-02 22:44 ` John Hubbard
2021-05-03 16:39 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:17 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 08/16] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations Logan Gunthorpe
2021-05-02 22:52 ` John Hubbard
2021-05-03 0:50 ` John Hubbard
2021-05-03 17:15 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 09/16] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg Logan Gunthorpe
2021-04-27 19:33 ` Jason Gunthorpe
2021-04-27 19:40 ` Jason Gunthorpe
2021-04-27 22:56 ` Logan Gunthorpe
2021-05-02 23:28 ` John Hubbard
2021-05-02 23:32 ` John Hubbard
2021-05-03 17:06 ` Logan Gunthorpe
2021-05-03 16:55 ` Logan Gunthorpe
2021-05-04 0:12 ` John Hubbard
2021-05-03 17:04 ` Logan Gunthorpe
2021-05-04 0:01 ` John Hubbard
2021-04-08 17:01 ` [PATCH 10/16] dma-mapping: Add flags to dma_map_ops to indicate PCI P2PDMA support Logan Gunthorpe
2021-05-03 0:32 ` John Hubbard
2021-05-03 17:09 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:19 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 11/16] iommu/dma: Support PCI P2PDMA pages in dma-iommu map_sg Logan Gunthorpe
2021-04-27 19:43 ` Jason Gunthorpe
2021-04-27 22:59 ` Logan Gunthorpe
2021-05-03 1:14 ` John Hubbard
2021-05-06 23:59 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:35 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 12/16] nvme-pci: Check DMA ops when indicating support for PCI P2PDMA Logan Gunthorpe
2021-05-03 1:29 ` John Hubbard
2021-05-03 17:17 ` Logan Gunthorpe
2021-05-04 0:17 ` John Hubbard
2021-04-08 17:01 ` [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for p2pdma pages Logan Gunthorpe
2021-05-03 1:34 ` John Hubbard
2021-05-03 17:19 ` Logan Gunthorpe
2021-05-04 0:26 ` John Hubbard
2021-04-08 17:01 ` [PATCH 14/16] nvme-rdma: Ensure dma support when using p2pdma Logan Gunthorpe
2021-04-27 19:47 ` Jason Gunthorpe
2021-04-27 22:59 ` Logan Gunthorpe
2021-05-03 1:37 ` John Hubbard
2021-04-08 17:01 ` [PATCH 15/16] RDMA/rw: use dma_map_sg_p2pdma() Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 16/16] PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg() Logan Gunthorpe
2021-04-27 19:28 ` [PATCH 00/16] Add new DMA mapping operation for P2PDMA Jason Gunthorpe
2021-04-27 20:21 ` John Hubbard
2021-04-27 20:48 ` Dan Williams
2021-05-02 1:22 ` John Hubbard
2021-05-11 16:05 ` Don Dutile
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