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Message-ID: <a61b0a48-d55b-494b-a7e8-04b02dc87e21@linux.dev>
Date: Mon, 21 Oct 2024 10:37:07 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Robin Murphy <robin.murphy@....com>, Christoph Hellwig <hch@....de>,
iommu@...ts.linux.dev
Cc: linux-trace-kernel@...r.kernel.org, Masami Hiramatsu
<mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Steven Rostedt <rostedt@...dmis.org>,
Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 3/3] dma-mapping: Trace more error paths
On 10/21/24 06:38, Robin Murphy wrote:
> On 2024-10-17 7:13 pm, Sean Anderson wrote:
>> It can be surprising to the user if DMA functions are only traced on
>> success. On failure, it can be unclear what the source of the problem
>> is. Fix this by tracing all functions even when they fail. Cases where
>> we BUG/WARN are skipped, since those should be sufficiently noisy
>> already.
>>
>> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
>> ---
>>
>> include/trace/events/dma.h | 41 ++++++++++++++++++++++++++++++++++++++
>> kernel/dma/mapping.c | 27 +++++++++++++++++--------
>> 2 files changed, 60 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h
>> index 9bc647f9ad4d..321cce327404 100644
>> --- a/include/trace/events/dma.h
>> +++ b/include/trace/events/dma.h
>> @@ -161,6 +161,12 @@ DEFINE_EVENT(_dma_alloc, dma_alloc_pages,
>> unsigned long attrs),
>> TP_ARGS(dev, virt_addr, dma_addr, size, dir, flags, attrs));
>> +DEFINE_EVENT(_dma_alloc, dma_alloc_sgt_err,
>> + TP_PROTO(struct device *dev, void *virt_addr, dma_addr_t dma_addr,
>> + size_t size, enum dma_data_direction dir, gfp_t flags,
>> + unsigned long attrs),
>> + TP_ARGS(dev, virt_addr, dma_addr, size, dir, flags, attrs));
>> +
>> TRACE_EVENT(dma_alloc_sgt,
>> TP_PROTO(struct device *dev, struct sg_table *sgt, size_t size,
>> enum dma_data_direction dir, gfp_t flags, unsigned long attrs),
>> @@ -325,6 +331,41 @@ TRACE_EVENT(dma_map_sg,
>> decode_dma_attrs(__entry->attrs))
>> );
>> +TRACE_EVENT(dma_map_sg_err,
>> + TP_PROTO(struct device *dev, struct scatterlist *sgl, int nents,
>> + int err, enum dma_data_direction dir, unsigned long attrs),
>> + TP_ARGS(dev, sgl, nents, err, dir, attrs),
>> +
>> + TP_STRUCT__entry(
>> + __string(device, dev_name(dev))
>> + __dynamic_array(u64, phys_addrs, nents)
>> + __field(int, err)
>> + __field(enum dma_data_direction, dir)
>> + __field(unsigned long, attrs)
>> + ),
>> +
>> + TP_fast_assign(
>> + struct scatterlist *sg;
>> + int i;
>> +
>> + __assign_str(device);
>> + for_each_sg(sgl, sg, nents, i)
>> + ((u64 *)__get_dynamic_array(phys_addrs))[i] = sg_phys(sg);
>> + __entry->err = err;
>> + __entry->dir = dir;
>> + __entry->attrs = attrs;
>> + ),
>> +
>> + TP_printk("%s dir=%s dma_addrs=%s err=%d attrs=%s",
>> + __get_str(device),
>> + decode_dma_data_direction(__entry->dir),
>> + __print_array(__get_dynamic_array(phys_addrs),
>> + __get_dynamic_array_len(phys_addrs) /
>> + sizeof(u64), sizeof(u64)),
>> + __entry->err,
>> + decode_dma_attrs(__entry->attrs))
>> +);
>> +
>> TRACE_EVENT(dma_unmap_sg,
>> TP_PROTO(struct device *dev, struct scatterlist *sgl, int nents,
>> enum dma_data_direction dir, unsigned long attrs),
>> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
>> index b8a6bc492fae..636dbb0629a4 100644
>> --- a/kernel/dma/mapping.c
>> +++ b/kernel/dma/mapping.c
>> @@ -223,6 +223,7 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
>> debug_dma_map_sg(dev, sg, nents, ents, dir, attrs);
>> } else if (WARN_ON_ONCE(ents != -EINVAL && ents != -ENOMEM &&
>> ents != -EIO && ents != -EREMOTEIO)) {
>> + trace_dma_map_sg_err(dev, sg, nents, ents, dir, attrs);
>
> Isn't this just a case of moving the existing tracepoint up outside the "if (ents > 0)" condition?
This is a separate tracepoint (_err) to simplify collecting/printing the
addresses.
>
>> return -EIO;
>> }
>> @@ -604,20 +605,26 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
>> if (WARN_ON_ONCE(flag & __GFP_COMP))
>> return NULL;
>> - if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
>> + if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr)) {
>> + trace_dma_alloc(dev, cpu_addr, *dma_handle, size,
>> + DMA_BIDIRECTIONAL, flag, attrs);
>> return cpu_addr;
>> + }
>> /* let the implementation decide on the zone to allocate from: */
>> flag &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
>> - if (dma_alloc_direct(dev, ops))
>> + if (dma_alloc_direct(dev, ops)) {
>> cpu_addr = dma_direct_alloc(dev, size, dma_handle, flag, attrs);
>> - else if (use_dma_iommu(dev))
>> + } else if (use_dma_iommu(dev)) {
>> cpu_addr = iommu_dma_alloc(dev, size, dma_handle, flag, attrs);
>> - else if (ops->alloc)
>> + } else if (ops->alloc) {
>> cpu_addr = ops->alloc(dev, size, dma_handle, flag, attrs);
>> - else
>> + } else {
>> + trace_dma_alloc(dev, NULL, 0, size, DMA_BIDIRECTIONAL, flag,
>> + attrs);
>> return NULL;
>
> Similarly just move this return down past the tracepoint, same as the hunk below?
OK
>> + }
>> trace_dma_alloc(dev, cpu_addr, *dma_handle, size, DMA_BIDIRECTIONAL,
>> flag, attrs);
>> @@ -642,11 +649,11 @@ void dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
>> */
>> WARN_ON(irqs_disabled());
>> - if (!cpu_addr)
>> - return;
>> -
>> trace_dma_free(dev, cpu_addr, dma_handle, size, DMA_BIDIRECTIONAL,
>> attrs);
>> + if (!cpu_addr)
>> + return;
>> +
>> debug_dma_free_coherent(dev, size, cpu_addr, dma_handle);
>> if (dma_alloc_direct(dev, ops))
>> dma_direct_free(dev, size, cpu_addr, dma_handle, attrs);
>> @@ -688,6 +695,8 @@ struct page *dma_alloc_pages(struct device *dev, size_t size,
>> trace_dma_alloc_pages(dev, page_to_virt(page), *dma_handle,
>> size, dir, gfp, 0);
>> debug_dma_map_page(dev, page, 0, size, dir, *dma_handle, 0);
>> + } else {
>> + trace_dma_alloc_pages(dev, NULL, 0, size, dir, gfp, 0);
>
> Could we move the page_to_virt() into the event definiton and let that handle NULL, then similarly hoist the tracepoint out of the condition?
Then we cannot reuse the event class for trace_dma_alloc, which does not
have a struct page available.
>> }
>> return page;
>> }
>> @@ -772,6 +781,8 @@ struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
>> sgt->nents = 1;
>> trace_dma_alloc_sgt(dev, sgt, size, dir, gfp, attrs);
>> debug_dma_map_sg(dev, sgt->sgl, sgt->orig_nents, 1, dir, attrs);
>> + } else {
>> + trace_dma_alloc_sgt_err(dev, NULL, 0, size, gfp, dir, attrs);
>
> And again similarly here - if I'm interested in calls to dma_alloc_contiguous(), I'd rather have a "dma_alloc_contiguous" tracepoint which can tell me both the arguments and the result at a glance, than have to remember to trace two distinct other things based on internal details.
Isn't it a case of just doing `perf record -e 'dma:dma_alloc_sgt*'`?
Fundamentally, these events have different information available, and
dealing with this in a generic manner is inconvenient.
--Sean
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