From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 769B130AABE; Fri, 26 Jun 2026 15:00:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782486058; cv=none; b=Pl1rK+vXtv+XP8jY7elN9ravgUcrxKgkUni4Q/7yPkczzHEOS8nlHgSKZfyNdVdVvOI1mOZYowmu8pOcX1iNUNznLlhRhFnq3jkqv6l/TTFTgA0MPkDWtu4Lo6/UCr/ZKIiDKOV38IoGrmIv1/frw/6vXuozBp1Pp4nHtf+mDj4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782486058; c=relaxed/simple; bh=XSs3CUva20TTxVS/K+HeZG9LbMIKRnbeFCP9OdmsvHA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YZDUPLWIIDRrUyJWEQ7bkhTCOm68EY/myN5dmb4w/FZx6LklzGJijiXhe6cu44iQdypTMfBcYuYoUNEgBkzCWO3nBgMXk2LdCm0JJ06acK840AjVs+5+ht1t1JsVSJ6LmIQxFT0pbE767Mu/9A91ldHcD4H1rqyA1Wcp4xLWs8c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nHoo2Yi/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nHoo2Yi/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D48E01F000E9; Fri, 26 Jun 2026 15:00:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782486055; bh=juC1Y5v1j3sP5fMQDkrZYHNSUJQ+4S5mJUHcpe7Ac+Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nHoo2Yi/y4ujBsFKNm/8GmcKx89Mae5+bQ7ujza84jDtcjvSs+ZUoVL69Boo7vGdk 8dMxUVeLpgwafnaKeZRD3TZp8e4ZtSG8lqn9Mp+jHxIjdPPx/R3ae/ZQMksOG/WTyg TE/mjtDb49CRf9bqw8oF9uoIPWqLpBwjtFyqazn6lpuFeiC1lpSDP0NUJoLeyUp/QK JHltctkNxct0riLSdhcwbrXAuyeFdoShcHwNnYhPyxw4qLzBGTBUTk7iUNgG3lXfAa CGPb1XNqC+Gj4LdIHL20+qPCy8Ef9+yq58//FqaxFz9FE1+B6ukmVUM3Bx1VffBvup g5G31jRhoyqug== Message-ID: Date: Fri, 26 Jun 2026 17:00:51 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 4/4] mm/slab: serialize defer_free_barrier() Content-Language: en-US To: "Harry Yoo (Oracle)" , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Alexei Starovoitov , Pedro Falcato Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org References: <20260624-kmalloc-nolock-fixes-v1-0-fdf4d17351dd@kernel.org> <20260624-kmalloc-nolock-fixes-v1-4-fdf4d17351dd@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/24/26 15:11, Harry Yoo (Oracle) wrote: > irq_work_sync() uses rcuwait instead of busy waiting in two cases: > > 1. The kernel is using PREEMPT_RT and the irq work does not run in a > hardirq context. > > 2. The architecture cannot send inter-processor interrupts to make > busy waiting reasonably short. > > However, rcuwait.h says: >> The caller is responsible for locking around rcuwait_wait_event(), >> and [prepare_to/finish]_rcuwait() such that writes to @task are >> properly serialized. > > Since defer_free_barrier() calls irq_work_sync() without any locks, > it can potentially cause a hang as writes to @task are not serialized. > > Fix this by calling defer_free_barrier() under slab_mutex and > cpus_read_lock() and add lockdep asserts. > > Now that defer_free_barrier() is called inside cpus_read_lock(), iterate > over online cpus instead of possible cpus. > > Reported-by: Sashiko > Closes: https://sashiko.dev/#/patchset/20260615-kfree_rcu_nolock-v3-0-70a54f3775bb%40kernel.org?part=5 > Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") > Cc: stable@vger.kernel.org > Signed-off-by: Harry Yoo (Oracle) Acked-by: Vlastimil Babka (SUSE) > --- > mm/slab_common.c | 5 ++--- > mm/slub.c | 6 +++++- > 2 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 388eb5980859..27f77273fabe 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -550,11 +550,10 @@ void kmem_cache_destroy(struct kmem_cache *s) > rcu_barrier(); > } > > - /* Wait for deferred work from kmalloc/kfree_nolock() */ > - defer_free_barrier(); > - > cpus_read_lock(); > mutex_lock(&slab_mutex); > + /* Wait for deferred work from kmalloc/kfree_nolock() */ > + defer_free_barrier(); > > s->refcount--; > if (s->refcount) { > diff --git a/mm/slub.c b/mm/slub.c > index 4a3618e3967e..52c8d3f33782 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6411,7 +6411,11 @@ void defer_free_barrier(void) > { > int cpu; > > - for_each_possible_cpu(cpu) > + /* irq_work_sync() may use rcuwait that requires serialization */ > + lockdep_assert_held(&slab_mutex); > + lockdep_assert_cpus_held(); > + > + for_each_online_cpu(cpu) > irq_work_sync(&per_cpu_ptr(&defer_free_objects, cpu)->work); > } > >