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Wed, 15 Oct 2025 15:46:16 -0700 (PDT) Date: Wed, 15 Oct 2025 15:46:13 -0700 From: "Vishal Moola (Oracle)" To: Sebastian Andrzej Siewior Cc: Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Clark Williams , Steven Rostedt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH] mempool: clarify behavior of mempool_alloc_preallocated() Message-ID: References: <20251014-mempool-doc-v1-1-bc9ebf169700@linutronix.de> <20251015192717.HvwzCChE@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251015192717.HvwzCChE@linutronix.de> On Wed, Oct 15, 2025 at 09:27:17PM +0200, Sebastian Andrzej Siewior wrote: > On 2025-10-15 11:52:24 [-0700], Vishal Moola (Oracle) wrote: > > > --- a/mm/mempool.c > > > +++ b/mm/mempool.c > > > @@ -461,8 +461,8 @@ EXPORT_SYMBOL(mempool_alloc_noprof); > > > * mempool_create(). > > > * > > > * This function is similar to mempool_alloc, but it only attempts allocating > > > - * an element from the preallocated elements. It does not sleep and immediately > > > - * returns if no preallocated elements are available. > > > + * an element from the preallocated elements. It only takes a single spinlock_t > > > > Might it make more sense to say "It may sleep" instead of "takes a > > single spinlock_t"? > > May sleep usually refers to something that can not be used in an > interrupt handler. Gotcha. > > I feel like the fact that we take a spinlock isn't the important part > > here (especially because we always drop it before returning). > It actually is. A spinlock_t can not be acquired in hardirq context or > when interrupts are explicitly disabled via local_irq_disable(). > Therefore you should use the function in a local_irq_disable() section. As someone not too familiar with how the locking intertwines with the scheduler contexts, seeing something like that makes much more sense to me than seeing "it only takes a single spinlock_t."