From: Alan Stern <stern@rowland.harvard.edu>
To: Harry Yoo <harry.yoo@oracle.com>
Cc: linux-mm@kvack.org, Dmitry Vyukov <dvyukov@google.com>,
lkmm@lists.linux.dev, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org,
Joel Fernandes <joelagnelf@nvidia.com>,
Daniel Lustig <dlustig@nvidia.com>,
Akira Yokosawa <akiyks@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Luc Maranget <luc.maranget@inria.fr>,
Jade Alglave <j.alglave@ucl.ac.uk>,
David Howells <dhowells@redhat.com>,
Nicholas Piggin <npiggin@gmail.com>,
Boqun Feng <boqun@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>,
Andrea Parri <parri.andrea@gmail.com>,
Pedro Falcato <pfalcato@suse.de>,
Vlastimil Babka <vbabka@suse.cz>,
Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
Hao Li <hao.li@linux.dev>, Shakeel Butt <shakeel.butt@linux.dev>,
Venkat Rao Bagalkote <venkat88@linux.ibm.com>,
Mateusz Guzik <mjguzik@gmail.com>,
Suren Baghdasaryan <surenb@google.com>,
Marco Elver <elver@google.com>
Subject: Re: [BUG] Memory ordering between kmalloc() and kfree()? it's confusing!
Date: Thu, 26 Feb 2026 11:42:02 -0500 [thread overview]
Message-ID: <d8308828-ed28-4650-8c8f-22a7e5cfd1a0@rowland.harvard.edu> (raw)
In-Reply-To: <aaByMLSAIJM8HdbO@hyeyoo>
On Fri, Feb 27, 2026 at 01:17:52AM +0900, Harry Yoo wrote:
> On Thu, Feb 26, 2026 at 10:45:55AM -0500, Alan Stern wrote:
> > On Thu, Feb 26, 2026 at 03:35:08PM +0900, Harry Yoo wrote:
> > > Because the slab allocator itself doesn't guarantee that such
> > > barriers are invoked within the allocator, it relies on users to
> > > do this when needed.
> >
> > It doesn't? Then how does the slab allocator guarantee that two
> > different CPUs won't try to perform allocations or deallocations from
> > the same slab at the same time, messing everything up?
>
> Ah, alloc/free slowpaths do use cmpxchg128 or spinlock and
> don't mess things up.
>
> But fastpath allocs/frees are served from percpu array that is protected
> by a local_lock. local_lock has a compiler barrier in it, but that's
> not enough.
If those things rely on a percpu array, how can one CPU possibly
manipulate a resource (slab or something else) that was changed by a
different CPU? The whole point of percpu data structures is that each
CPU gets its own copy.
Alan Stern
next prev parent reply other threads:[~2026-02-26 16:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-26 6:35 Harry Yoo
2026-02-26 15:45 ` Alan Stern
2026-02-26 16:17 ` Harry Yoo
2026-02-26 16:42 ` Alan Stern [this message]
2026-02-26 17:11 ` Harry Yoo
2026-02-26 18:06 ` Alan Stern
2026-02-26 17:59 ` Christoph Lameter (Ampere)
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