linux.git/kernel/dma/debug.c, branch v5.10.194

dma-debug: make things less spammy under memory pressure

2022-06-22T12:13:13+00:00

[ Upstream commit e19f8fa6ce1ca9b8b934ba7d2e8f34c95abc6e60 ]

Limit the error msg to avoid flooding the console.  If you have a lot of
threads hitting this at once, they could have already gotten passed the
dma_debug_disabled() check before they get to the point of allocation
failure, resulting in quite a lot of this error message spamming the
log.  Use pr_err_once() to limit that.

Signed-off-by: Rob Clark 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

dma-debug: change allocation mode from GFP_NOWAIT to GFP_ATIOMIC

2022-06-09T08:20:54+00:00

[ Upstream commit 84bc4f1dbbbb5f8aa68706a96711dccb28b518e5 ]

We observed the error "cacheline tracking ENOMEM, dma-debug disabled"
during a light system load (copying some files). The reason for this error
is that the dma_active_cacheline radix tree uses GFP_NOWAIT allocation -
so it can't access the emergency memory reserves and it fails as soon as
anybody reaches the watermark.

This patch changes GFP_NOWAIT to GFP_ATOMIC, so that it can access the
emergency memory reserves.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

dma-debug: fix return value of __setup handlers

2022-04-08T12:40:25+00:00

[ Upstream commit 80e4390981618e290616dbd06ea190d4576f219d ]

When valid kernel command line parameters
  dma_debug=off dma_debug_entries=100
are used, they are reported as Unknown parameters and added to init's
environment strings, polluting it.

  Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc5
    dma_debug=off dma_debug_entries=100", will be passed to user space.

and

 Run /sbin/init as init process
   with arguments:
     /sbin/init
   with environment:
     HOME=/
     TERM=linux
     BOOT_IMAGE=/boot/bzImage-517rc5
     dma_debug=off
     dma_debug_entries=100

Return 1 from these __setup handlers to indicate that the command line
option has been handled.

Fixes: 59d3daafa1726 ("dma-debug: add kernel command line parameters")
Signed-off-by: Randy Dunlap 
Reported-by: Igor Zhbanov 
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: Joerg Roedel 
Cc: Christoph Hellwig 
Cc: Marek Szyprowski 
Cc: iommu@lists.linux-foundation.org
Cc: Robin Murphy 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

dma-debug: fix sg checks in debug_dma_map_sg()

2021-10-27T07:56:47+00:00

[ Upstream commit 293d92cbbd2418ca2ba43fed07f1b92e884d1c77 ]

The following warning occurred sporadically on s390:
DMA-API: nvme 0006:00:00.0: device driver maps memory from kernel text or rodata [addr=0000000048cc5e2f] [len=131072]
WARNING: CPU: 4 PID: 825 at kernel/dma/debug.c:1083 check_for_illegal_area+0xa8/0x138

It is a false-positive warning, due to broken logic in debug_dma_map_sg().
check_for_illegal_area() checks for overlay of sg elements with kernel text
or rodata. It is called with sg_dma_len(s) instead of s->length as
parameter. After the call to ->map_sg(), sg_dma_len() will contain the
length of possibly combined sg elements in the DMA address space, and not
the individual sg element length, which would be s->length.

The check will then use the physical start address of an sg element, and
add the DMA length for the overlap check, which could result in the false
warning, because the DMA length can be larger than the actual single sg
element length.

In addition, the call to check_for_illegal_area() happens in the iteration
over mapped_ents, which will not include all individual sg elements if
any of them were combined in ->map_sg().

Fix this by using s->length instead of sg_dma_len(s). Also put the call to
check_for_illegal_area() in a separate loop, iterating over all the
individual sg elements ("nents" instead of "mapped_ents").

While at it, as suggested by Robin Murphy, also move check_for_stack()
inside the new loop, as it is similarly concerned with validating the
individual sg elements.

Link: https://lore.kernel.org/lkml/20210705185252.4074653-1-gerald.schaefer@linux.ibm.com
Fixes: 884d05970bfb ("dma-debug: use sg_dma_len accessor")
Signed-off-by: Gerald Schaefer 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

dma-debug: fix debugfs initialization order

2021-09-18T11:40:13+00:00

[ Upstream commit 173735c346c412d9f084825ecb04f24ada0e2986 ]

Due to link order, dma_debug_init is called before debugfs has a chance
to initialize (via debugfs_init which also happens in the core initcall
stage), so the directories for dma-debug are never created.

Decouple dma_debug_fs_init from dma_debug_init and defer its init until
core_initcall_sync (after debugfs has been initialized) while letting
dma-debug initialization occur as soon as possible to catch any early
mappings, as suggested in [1].

[1] https://lore.kernel.org/linux-iommu/YIgGa6yF%2Fadg8OSN@kroah.com/

Fixes: 15b28bbcd567 ("dma-debug: move initialization to common code")
Signed-off-by: Anthony Iliopoulos 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

dma-mapping: move dma-debug.h to kernel/dma/

2020-10-06T05:07:05+00:00

Most of dma-debug.h is not required by anything outside of kernel/dma.
Move the four declarations needed by dma-mappin.h or dma-ops providers
into dma-mapping.h and dma-map-ops.h, and move the remainder of the
file to kernel/dma/debug.h.

Signed-off-by: Christoph Hellwig

dma-debug: convert comma to semicolon

2020-09-21T14:48:38+00:00

Replace a comma between expression statements by a semicolon.

Signed-off-by: Xu Wang 
Signed-off-by: Christoph Hellwig

dma-debug: remove most exports

2020-09-11T06:13:12+00:00

Now that the main dma mapping entry points are out of line most of the
symbols in dma-debug.c can only be called from built-in code.  Remove
the unused exports.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Robin Murphy

dma-debug: remove debug_dma_assert_idle() function

2020-08-14T22:22:43+00:00

This remoes the code from the COW path to call debug_dma_assert_idle(),
which was added many years ago.

Google shows that it hasn't caught anything in the 6+ years we've had it
apart from a false positive, and Hugh just noticed how it had a very
unfortunate spinlock serialization in the COW path.

He fixed that issue the previous commit (a85ffd59bd36: "dma-debug: fix
debug_dma_assert_idle(), use rcu_read_lock()"), but let's see if anybody
even notices when we remove this function entirely.

NOTE! We keep the dma tracking infrastructure that was added by the
commit that introduced it.  Partly to make it easier to resurrect this
debug code if we ever deside to, and partly because that tracking by pfn
and offset looks quite reasonable.

The problem with this debug code was simply that it was expensive and
didn't seem worth it, not that it was wrong per se.

Acked-by: Dan Williams 
Acked-by: Christoph Hellwig 
Signed-off-by: Linus Torvalds

dma-debug: fix debug_dma_assert_idle(), use rcu_read_lock()

2020-08-14T22:16:03+00:00

Since commit 2a9127fcf229 ("mm: rewrite wait_on_page_bit_common()
logic") improved unlock_page(), it has become more noticeable how
cow_user_page() in a kernel with CONFIG_DMA_API_DEBUG=y can create and
suffer from heavy contention on DMA debug's radix_lock in
debug_dma_assert_idle().

It is only doing a lookup: use rcu_read_lock() and rcu_read_unlock()
instead; though that does require the static ents[] to be moved
onstack...

...but, hold on, isn't that radix_tree_gang_lookup() and loop doing
quite the wrong thing: searching CACHELINES_PER_PAGE entries for an
exact match with the first cacheline of the page in question?
radix_tree_gang_lookup() is the right tool for the job, but we need
nothing more than to check the first entry it can find, reporting if
that falls anywhere within the page.

(Is RCU safe here? As safe as using the spinlock was. The entries are
never freed, so don't need to be freed by RCU. They may be reused, and
there is a faint chance of a race, with an offending entry reused while
printing its error info; but the spinlock did not prevent that either,
and I agree that it's not worth worrying about. ]

[ Side noe: this patch is a clear improvement to the status quo, but the
  next patch will be removing this debug function entirely.

  But just in case we decide we want to resurrect the debugging code
  some day, I'm first applying this improvement patch so that it doesn't
  get lost    - Linus ]

Fixes: 3b7a6418c749 ("dma debug: account for cachelines and read-only mappings in overlap tracking")
Signed-off-by: Hugh Dickins 
Acked-by: Dan Williams 
Acked-by: Christoph Hellwig 
Signed-off-by: Linus Torvalds