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Message-ID: <1348676613.4020.13.camel@lorien2>
Date: Wed, 26 Sep 2012 10:23:33 -0600
From: Shuah Khan <shuah.khan@...com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: joerg.roedel@....com, tglx@...utronix.de, mingo@...hat.com,
hpa@...or.com, rob@...dley.net, akpm@...ux-foundation.org,
bhelgaas@...gle.com, stern@...land.harvard.edu,
LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
devel@...uxdriverproject.org, x86@...nel.org, shuahkhan@...il.com
Subject: Re: [PATCH v2] dma-debug: New interfaces to debug dma mapping errors
On Wed, 2012-09-26 at 09:12 -0400, Konrad Rzeszutek Wilk wrote:
> >
>
> Thanks for improving this patch. It is looking more and more ready for
> the kernel. With that in mind, I've some comments below.
Good. Thanks for the comments and good suggestions. Will work on v3.
>
> >
> >
> > --- a/lib/dma-debug.c
> > +++ b/lib/dma-debug.c
> > @@ -57,6 +57,7 @@ struct dma_debug_entry {
> > int direction;
> > int sg_call_ents;
> > int sg_mapped_ents;
> > + int dma_map_error_flag;
>
> I don't think you need 'dma_map' as a prefix a this is in an
> dma_debug structure. Perhaps 'map_error_cnt' ?
I can drop dma prefix from all the counts I added.
>
> But looking at the implementation this is actually an enum?
> Can you do this instead:
>
> enum map_err_type map_err_type;
Correct. It can be a enum type.
> ?
>
> > #ifdef CONFIG_STACKTRACE
> > struct stack_trace stacktrace;
> > unsigned long st_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
> > @@ -83,6 +84,11 @@ static u32 global_disable __read_mostly;
> > /* Global error count */
> > static u32 error_count;
> >
> > +/* dma mapping error counts */
> > +static u32 dma_map_errors;
> > +static u32 dma_map_errors_not_checked;
> > +static u32 dma_unmap_errors;
>
> s/dma//
Will drop dma prefix here.
>
> > +
> > /* Global error show enable*/
> > static u32 show_all_errors __read_mostly;
> > /* Number of errors to show */
> > @@ -104,6 +110,9 @@ static struct dentry *show_num_errors_dent __read_mostly;
> > static struct dentry *num_free_entries_dent __read_mostly;
> > static struct dentry *min_free_entries_dent __read_mostly;
> > static struct dentry *filter_dent __read_mostly;
> > +static struct dentry *dma_map_errors_dent __read_mostly;
> > +static struct dentry *dma_map_errors_not_checked_dent __read_mostly;
> > +static struct dentry *dma_unmap_errors_dent __read_mostly;
>
> Ditto.
ok
>
> >
> > /* per-driver filter related state */
> >
> > @@ -120,6 +129,15 @@ static const char *type2name[4] = { "single", "page",
> > static const char *dir2name[4] = { "DMA_BIDIRECTIONAL", "DMA_TO_DEVICE",
> > "DMA_FROM_DEVICE", "DMA_NONE" };
> >
> > +enum {
> > + dma_map_error_check_not_applicable,
> > + dma_map_error_not_checked,
> > + dma_map_error_checked,
> > +};
>
> s/dma//
> s/error/err//
>
> And perhaps make them uppercase?
Yup. Uppercase will be in line with the general enum convention.
>
> Can you name the enum? Say 'map_err_types'
>
>
> > +static const char *maperr2str[3] = { "dma map error check not applicable",
> > + "dma map error not checked",
> > + "dma map error checked" };
> > +
>
> Just do this:
>
> static const char *const names[] = {
> [err_check_na] = {"check n/a"},
> [err_not_checked] = {"not checked"},
> .. snip..
> };
>
yes. Will work better than the current.
> That way you don't have to worry about the size and can just
> use ARRAY_SIZE(names) to check for valid enum size.
>
> > /* little merge helper - remove it after the merge window */
> > #ifndef BUS_NOTIFY_UNBOUND_DRIVER
> > #define BUS_NOTIFY_UNBOUND_DRIVER 0x0005
> > @@ -381,11 +399,12 @@ void debug_dma_dump_mappings(struct device *dev)
> > list_for_each_entry(entry, &bucket->list, list) {
> > if (!dev || dev == entry->dev) {
> > dev_info(entry->dev,
> > - "%s idx %d P=%Lx D=%Lx L=%Lx %s\n",
> > + "%s idx %d P=%Lx D=%Lx L=%Lx %s %s\n",
> > type2name[entry->type], idx,
> > (unsigned long long)entry->paddr,
> > entry->dev_addr, entry->size,
> > - dir2name[entry->direction]);
> > + dir2name[entry->direction],
> > + maperr2str[entry->dma_map_error_flag]);
> > }
> > }
> >
> > @@ -695,6 +714,28 @@ static int dma_debug_fs_init(void)
> > if (!filter_dent)
> > goto out_err;
> >
> > + dma_map_errors_dent = debugfs_create_u32("dma_map_errors", 0444,
>
> Just call it 'map_errors'
>
> > + dma_debug_dent,
> > + &dma_map_errors);
> > +
> > + if (!dma_map_errors_dent)
> > + goto out_err;
> > +
> > + dma_map_errors_not_checked_dent = debugfs_create_u32(
> > + "dma_map_errors_not_checked",
>
> Ditto. s/dma//
> > + 0444,
> > + dma_debug_dent,
> > + &dma_map_errors_not_checked);
> > +
> > + if (!dma_map_errors_not_checked_dent)
> > + goto out_err;
> > +
> > + dma_unmap_errors_dent = debugfs_create_u32("dma_unmap_errors", 0444,
>
> s/dma//
> > + dma_debug_dent,
> > + &dma_unmap_errors);
> > + if (!dma_unmap_errors_dent)
> > + goto out_err;
> > +
>
> This whole function could use a a loop to set this up instead of doing
> one by one... But that is another patch that can be done later.
Yes.
>
> > return 0;
> >
> > out_err:
> > @@ -849,7 +890,8 @@ static void check_unmap(struct dma_debug_entry *ref)
> > struct hash_bucket *bucket;
> > unsigned long flags;
> >
> > - if (dma_mapping_error(ref->dev, ref->dev_addr)) {
> > + if (ref->dev_addr == DMA_ERROR_CODE) {
>
> The DMA_ERROR_CODE is not exported on every architecture. Worst yet,
> it is not used universally on all IOMMUs - if you look in the GART
> (gart_mapping_error) it does not check for the DMA_ERROR_CODE but for
> its own bad_dma_addr address. I think using the dma_mapping_errors here
> is still a good idea.
Good point.
>
> > + dma_unmap_errors += 1;
> > err_printk(ref->dev, NULL, "DMA-API: device driver tries "
> > "to free an invalid DMA memory address\n");
> > return;
> > @@ -915,6 +957,15 @@ static void check_unmap(struct dma_debug_entry *ref)
> > dir2name[ref->direction]);
> > }
> >
> > + if (entry->dma_map_error_flag == dma_map_error_not_checked) {
>
> Wait. Aren't you using dma_map_error_flag to only be up to 3 - as you
> are using it to lookup in the string table for its proper name?
>
> Perhaps the string table lookup should use a different flag??
>
> > + err_printk(ref->dev, entry,
> > + "DMA-API: device driver failed to check map error"
> > + "[device address=0x%016llx] [size=%llu bytes] "
> > + "[mapped as %s]",
> > + ref->dev_addr, ref->size,
> > + type2name[entry->type]);
> > + }
> > +
> > hash_bucket_del(entry);
> > dma_entry_free(entry);
> >
> > @@ -1022,8 +1073,11 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
> > if (unlikely(global_disable))
> > return;
> >
> > - if (unlikely(dma_mapping_error(dev, dma_addr)))
> > + if (dma_addr == DMA_ERROR_CODE) {
>
> Ditto
> > + dma_map_errors += 1;
> > + dma_map_errors_not_checked += 1;
> > return;
> > + }
> >
> > entry = dma_entry_alloc();
> > if (!entry)
> > @@ -1035,6 +1089,7 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
> > entry->dev_addr = dma_addr;
> > entry->size = size;
> > entry->direction = direction;
> > + entry->dma_map_error_flag = dma_map_error_not_checked;
>
> So if it is greater than three, then maperr2str[entry->dma_map_error_flag] is going
> to blow up, right?
Yeah. It shouldn't, but would be good to check.
>
> >
> > if (map_single)
> > entry->type = dma_debug_single;
> > @@ -1050,6 +1105,35 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
> > }
> > EXPORT_SYMBOL(debug_dma_map_page);
> >
> > +void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
> > +{
> > + struct dma_debug_entry ref;
> > + struct dma_debug_entry *entry;
> > + struct hash_bucket *bucket;
> > + unsigned long flags;
> > +
> > + if (unlikely(global_disable))
> > + return;
> > +
> > + if (dma_addr == DMA_ERROR_CODE) {
>
> Don't use that... Just the IOMMUs' dma_mapping_error call..
>
> > + dma_map_errors_not_checked -= 1;
>
> Should you check in case the user calls dma_mapping_error more than once on
> the same dma_addr?
Correct. Check is needed especially coupled with dma-debug internal use
of dma_mapping_error().
>
> > + return;
> > + }
> > +
> > + ref.dev = dev;
> > + ref.dev_addr = dma_addr;
> > + bucket = get_hash_bucket(&ref, &flags);
> > + entry = bucket_find_exact(bucket, &ref);
> > +
> > + if (!entry) /* very likley dma-api didn't call debug_dma_map_page() */
>
> Ok, so should we re-adjust dma_map_errors_not_checked? Or we
> don't care?
>
> > + goto out;
> > +
> > + entry->dma_map_error_flag = dma_map_error_checked;
> > +out:
> > + put_hash_bucket(bucket, &flags);
> > +}
> > +EXPORT_SYMBOL(debug_dma_mapping_error);
> > +
> > void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
> > size_t size, int direction, bool map_single)
> > {
> > --
> > 1.7.9.5
> >
> >
> >
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