On 6/24/26 10:41 PM, Pedro Falcato wrote: > On Mon, Jun 15, 2026 at 08:05:56PM +0900, Harry Yoo (Oracle) wrote: >> Since kmalloc_nolock() always fails in NMI and hardirq contexts on >> PREEMPT_RT, slub_kunit cannot properly test _nolock() APIs. >> >> Register a kprobe pre-handler to invoke kmalloc_nolock() and >> kfree_nolock() in the middle of the slab allocator. However, do not >> register the handler on UP kernels [1]. > > Maybe explain in the commit message why that is?
Because it's the case is broken on UP and we decided not bother to fix. Thought the cover letter in Link: would give enough context. >> To attach the pre-handler while s->cpu_sheaves->lock or n->list_lock >> is held, add a wrapper function for lockdep_assert_held() that calls >> a no-op function slab_attach_kprobe_locked() on debug builds. The > > Why lockdep? I wanted to avoid hard-coding internal slab function names in the test module while having a good coverage. > Wouldn't it make more sense to add these triggers after> locking these locks? Good point. Perhaps it'd make more sense to let _trylock() fail occasionally, because that what I actually want to test. >> function is optimized away when neither CONFIG_PROVE_LOCKING nor >> CONFIG_DEBUG_VM is selected and register_kprobe() fails. >> >> The function calls barrier() to prevent the compiler from optimizing >> away its callsites. Otherwise, the compiler may consider the function >> does not have any side effect and remove callsites. > > My wider comment is the following: this looks very useful but perhaps should > be lifted to Kunit itself? There's already function redirection (which could > be used for this as well). TIL kunit function redirection, thanks :) > I don't know if that suits your purposes? Hmm, but looking at the kunit function redirection, apparently the function needs to have a symbol to redirect. Not sure how feasible it is to make all those lock helpers have symbols to use kunit function redirection. > Choosing to say "I want to hook this random function using kprobe and give > it custom behavior" sounds lovely for all sorts of testing. Sounds lovely. Actually, I was thinking it would be lovely to have fault-injection-like feature for memcg because it's hard to trigger that in kunit... Thanks! -- Cheers, Harry / Hyeonggon
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