On Tue, Jun 8, 2021 at 1:47 AM <glittao@xxxxxxxxx> wrote: > > From: Oliver Glitta <glittao@xxxxxxxxx> > > Add documentation for a KUnit test for SLUB debugging functionality. > > Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx> I'm not in the intended audience for this documentation, so I've mainly just gone and pointed out some small spelling mistakes and some formatting suggestions. > --- > Documentation/vm/slub.rst | 104 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 104 insertions(+) > > diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst > index 03f294a638bd..ca82fc1649ee 100644 > --- a/Documentation/vm/slub.rst > +++ b/Documentation/vm/slub.rst > @@ -384,5 +384,109 @@ c) Execute ``slabinfo-gnuplot.sh`` in '-t' mode, passing all of the > 40,60`` range will plot only samples collected between 40th and > 60th seconds). > > +KUnit tests for SLUB debugging functionality > +============================================ > + > +These KUnit tests are used to test some of the SLUB debugging > +functionalities. > + > +KUnit tests are used for unit testing in Linux kernel and easy to run, > +so it is probably the best choice for this type of tests. Note: if we think KUnit is worth explaining here, perhaps it's also worth linking to KUnit documentation? Something like "KUnit (Documentation/dev-tools/kunit/index.rst) ..." should work, or "See KUnit documentation (...) for more details", etc. > + > +There are tests, which corrupt redzone, the free objects and the freelist. > +Tests are corrupting specific bytes in cache and checking if validation > +finds expected number of bugs. Bug reports are silenced. > + > +Config option > + > +In order to built and then run this tests you need to switch nit: "to build" nit: "run these tests" > +option SLUB_KUNIT_TEST on. It is tristate option so it can also minor nit: s/is tristate/is a tristate > +be built as a module. This option depends on SLUB_DEBUG and > +KUNIT options. By default it is on with all kunit tests. I assume this last sentence is about CONFIG_KUNIT_ALL_TESTS. I don't think we need to document that here. It could also mislead users as selecting CONFIG_KUNIT_ALL_TESTS=y will not be sufficient to make the test run on its own. > + > +Error counting > + > +To get number of errors discovered in slub is used test API kunit_resource. Nit: "To get the number" Nit: can we use ``kunit_resource`` to format code-related terms? Note: we can link to the API reference by including "test API (Documentation/dev-tools/kunit/api/test.rst)" Not sure if you saw, but this is that page: https://www.kernel.org/doc/html/latest/dev-tools/kunit/api/test.html Coincidentally enough, kunit_resource is the first thing shown for now :) Note: it'd be cool if we could link to a specific section, but I haven't checked if that's actually possible with automarkup.py, e.g. like https://www.kernel.org/doc/html/latest/dev-tools/kunit/api/test.html#c.kunit_resource > +In test_init the reference to the integer variable slab_errors is added > +to the resource of this tests. > + > +During slub cache checking always when bug should be reported or fixed function Nit: "when a bug" > +slab_add_kunit_errors() is called. This function find resource to kunit test > +and increment value of data in founded resource, which is slab_errors > +variable. > + > +Silence bug reports > + > +The function slab_add_kunit_errors() is returning bool, which is true if there is kunit test > +with correct kunit_resource running, to silence bug reports, so they are not printed. > +We do not want to correct errors we only want to know they occurred, so these reports > +are unnnecessary. nit: "unnecessary" > + > +KASAN option > + > +Only 2 out of 5 tests are runnig with KASAN option is on. nit: "running" > +The other three tests deliberately modifies non-allocated objects. And KASAN nit: "other three tests ... modify" > +does not detect some errors in the same way as SLUB_DEBUG. So, these tests > +does not run when KASAN option is on. > + > +TESTS I'm not the intended target for this doc, so feel free to ignore this comment entirely. Hmm, I'm not really a fan of the docs listing out each test case and what they do. I feel like this will get out of sync and you now are expected to read another file to understand what the tests do. I can see the benefit of a high-level explanation, especially if we started having more tests scattered across multiple files, but I think we should wait until that time comes. So I'd personally prefer it if we converted these sections into comments on the test cases themselves. > + > +1. test_clobber_zone > + > + SLUB cache with SLUB_REDZONE flag can detects writings after object. This nit: is there a missing word after "after object.", perhaps "deallocation"? Perhaps then: "can detect writes after objection deallocation", or more simply "can detect write-after-free errors" ? > + functionality is tested here on allocated memory. > + > + First, there is allocated memory with SLAB_REDZONE and then the first byte > + after allocated space is modified. Validation founds 2 errors, because of > + the bug and the fix of the memory. > + > + > +2. test_next_pointer > + > + SLUB have list of free objects and the address of the next free object > + is always saved in free object at offset specified in variable offset > + in struct kmem_cache. This test try to corrupt this freelist and > + then correct it. > + > + First, there is allocated and freed memory to get a pointer to free object. > + After that, the pointer to next free object is corrupted. The first validation finds > + 3 errors. One for corrupted freechain, the second for the wrong count of objects > + in use and the third for fixing the issue. This fix only set number of objects > + in use to a number of all objects minus 1, because the first free object > + was corrupted. > + > + Then the free pointer is fixed to his previous value. The second validation finds > + 2 errors. One for the wrong count of objects in use and one for fixing this error. > + > + Last validation is used to check if all errors were corrected so no error > + is found. > + > +3. test_first_word > + > + SLUB cache with SLAB_POISON flag can detect poisoning free objects. This > + functionality is tested in this test. The test tries to corrupt > + the first byte in freed memory. > + > + First of all, memory is allocated and freed to get a pointer to a free object > + and then the first byte is corrupted. After that, validation finds 2 errors, > + one for the bug and the other one for the fix of the memory. > + > +4. test_clobber_50th_byte > + > + In this test SLAB_POISON functionality is tested. The test tries to > + corrupt the 50th byte in freed memory. > + > + First, pointer to a free memory is acquired by allocating and freeing memory. > + Then 50th byte is corrupted and validation finds 2 errors for the bug and > + the fix of the memory. > + > +5. test_clobber_redzone_free > + > + This test tests redzone functionality of SLUB cache on a freed object. > + > + First, it gets pointer to the free object with allocating and freeing and > + then corrupts the first byte after the freed object. Validation finds > + 2 errors for the bug and the fix of the memory. > + > Christoph Lameter, May 30, 2007 > Sergey Senozhatsky, October 23, 2015 > -- > 2.31.1.272.g89b43f80a5 > > -- > You received this message because you are subscribed to the Google Groups "KUnit Development" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kunit-dev+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/kunit-dev/20210608084740.6282-1-glittao%40gmail.com.
