Some spelling fixes below but it got a bit much when looking through this. Maybe rewrite this again for clarity? On Tue, 8 Jun 2021, glittao@xxxxxxxxx wrote: > +KUnit tests for SLUB debugging functionality > +============================================ > + > +These KUnit tests are used to test some of the SLUB debugging > +functionalities. functionality. > + > +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. > + > +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. "in a SLUB cache" .... or "in a cache" finds *the* expected number of ... > +In order to built and then run this tests you need to switch > +option SLUB_KUNIT_TEST on. It is tristate option so it can also *the* option *a* tristate option > +be built as a module. This option depends on SLUB_DEBUG and > +KUNIT options. By default it is on with all kunit tests. > + > +Error counting > + > +To get number of errors discovered in slub is used test API kunit_resource. What does that mean? > +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 > +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. These reports are unnecessary because we do not want to correct errors. We only want to know that they occurred. > + > +KASAN option > + > +Only 2 out of 5 tests are runnig with KASAN option is on. running > +The other three tests deliberately modifies non-allocated objects. And KASAN modify > +does not detect some errors in the same way as SLUB_DEBUG. So, these tests > +does not run when KASAN option is on. do > +1. test_clobber_zone > + > + SLUB cache with SLUB_REDZONE flag can detects writings after object. This > + functionality is tested here on allocated memory. ... can detect modifying memory locations after the object. > + > + 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. after *the* allocated space. The validation finds 2 errors. One is the fact that there is a corrupted redzone and the second due to the repair of the redzone. > +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. SLUB *has a* .... is ** saved in a *freed object* at *the* offset ... > + > + 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 >
