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 GEr7Di/9 OBudUDOHWQgVM5NmhXJywmhKlkD6uDWJNv5U+5OTPwO1GY3HThBQcRYcl9eufU+wmljkwsaycvD07Gn9KZXf7zypY+HqsdyY7HsYa9TbYe+t9oBq5n6umnw05n37ZUfwSlE1XnCmgB9fC7635YUaaV5RDaiz3US+oVpGKpdRawE/N4Bra3UKz792oEa4kIifd7ThV2gpwLDr6gGo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 10, 2025 at 11:36:02AM +0200, Vlastimil Babka wrote: > On 7/9/25 03:53, Alexei Starovoitov wrote: > > From: Alexei Starovoitov > > > > kmalloc_nolock() relies on ability of local_lock to detect the situation > > when it's locked. > > In !PREEMPT_RT local_lock_is_locked() is true only when NMI happened in > > irq saved region that protects _that specific_ per-cpu kmem_cache_cpu. > > In that case retry the operation in a different kmalloc bucket. > > The second attempt will likely succeed, since this cpu locked > > different kmem_cache_cpu. > > > > Similarly, in PREEMPT_RT local_lock_is_locked() returns true when > > per-cpu rt_spin_lock is locked by current task. In this case re-entrance > > into the same kmalloc bucket is unsafe, and kmalloc_nolock() tries > > a different bucket that is most likely is not locked by the current > > task. Though it may be locked by a different task it's safe to > > rt_spin_lock() on it. > > > > Similar to alloc_pages_nolock() the kmalloc_nolock() returns NULL > > immediately if called from hard irq or NMI in PREEMPT_RT. > > > > kfree_nolock() defers freeing to irq_work when local_lock_is_locked() > > and in_nmi() or in PREEMPT_RT. > > > > SLUB_TINY config doesn't use local_lock_is_locked() and relies on > > spin_trylock_irqsave(&n->list_lock) to allocate while kfree_nolock() > > always defers to irq_work. > > > > Signed-off-by: Alexei Starovoitov > > @@ -3911,6 +3953,12 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > > void *flush_freelist = c->freelist; > > struct slab *flush_slab = c->slab; > > > > + if (unlikely(!allow_spin)) > > + /* > > + * Reentrant slub cannot take locks > > + * necessary for deactivate_slab() > > + */ > > + return NULL; > > Hm but this is leaking the slab we allocated and have in the "slab" > variable, we need to free it back in that case. But it might be a partial slab taken from the list? Then we need to trylock n->list_lock and if that fails, oh... > > c->slab = NULL; > > c->freelist = NULL; > > c->tid = next_tid(c->tid); -- Cheers, Harry / Hyeonggon