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owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 17, 2025 at 04:02:25PM +0900, Harry Yoo wrote: > On Tue, Sep 16, 2025 at 01:26:53PM -0700, Alexei Starovoitov wrote: > > On Tue, Sep 16, 2025 at 12:06 PM Vlastimil Babka wrote: > > > > It's ok to call __update_cpu_freelist_fast(). It won't break anything. > > > > Because only nmi can make this cpu to be in the middle of freelist update. > > > > > > You're right, freeing uses the "slowpath" (local_lock protected instead of > > > cmpxchg16b) c->freelist manipulation only on RT. So we can't preempt it with > > > a kprobe on !RT because it doesn't exist there at all. > > Right. > > > > The only one is in ___slab_alloc() and that's covered. > > Right. > > and this is a question not relevant to reentrant kmalloc: > > On PREEMPT_RT, disabling fastpath in the alloc path makes sense because > both paths updates c->freelist, but in the free path, by disabling the > lockless fastpath, what are we protecting against? > > the free fastpath updates c->freelist but not slab->freelist, and > the free slowpath updates slab->freelist but not c->freelist? > > I failed to imagine how things can go wrong if we enable the lockless > fastpath in the free path. Oops, sorry. it slipped my mind. Things can go wrong if the free fastpath is executed while the alloc slowpath is executing and gets preempted. -- Cheers, Harry / Hyeonggon