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 61D43442B11 for ; Wed, 5 Aug 2026 12:26:27 +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=1785932788; cv=none; b=PXvRUXzBAzI+bg+yUrFwo8T5LG1asz62L9ZhlD6Drla3l7AkNPa9/Qa854p+t1swyNAd4E68nHhZHY0hQ5g9u3H7HXdGpg4j7UyrZKqPYpncSkJoqMuBdypG7a6ZtR+LJKYeVfdtZhrQd5sElZ6P8//SGwVgGet5uj9JwMZx428= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785932788; c=relaxed/simple; bh=UHnifuziA6Oh5dRuA4KvLYUEsgwk3fm+FfA/dnGI0rg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cyAQLrwSuWLZ+36EzaY9hVpfIDwnlo5dWcvC3Y9/78uMKM462xuVhTwNblmc/Skyo2K9OnSG4+42c3b7L8yYzcUeLxSDZHqO+WB/oAt5M79KngooBitR4xnsuxNkJ3FQSqAXlaC3jeCYoPZnLdqMTG2maAQ3FHBClxOx43kDtBI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Dg6zYRc/; 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="Dg6zYRc/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB18C1F000E9; Wed, 5 Aug 2026 12:26:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785932787; bh=IlmD8FVPU9Qx/uX6OcnYNun+6FlLqKRo+qT2MOzGSIU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Dg6zYRc/F+HXAaWcCH3YDVw+oVkVy5xQ843u9Mg06P1nQWAODPPiN69tCAOSUMWFx xNX8IwFsVAAuXKL/HgvcaLVCd+mb08xFxHXEBujJsfJB3GcM2/b39+TlflP1VI8wZg Oun4Re1ly9m4dFRtaERiX8xfVxv2HIWSxgF/+o3h7S53fXvv3T/nMTL94ZiitMDXwP mF5j3ByA3FNuZOUj3lhyYvzai1k9zQHyd0tOB+cYpXrEfbvYeumkVc4ogzE8EsI7qZ qoB/R+7NdsLygrWoKlg5rInGhPPscapYMQLQfRXsCXkk7ZDBj0lXpJCtN0vyRNmSWS OmNJXco9KW1qA== Message-ID: <6bb83027-07fb-4152-8edd-f349e6fbcc42@kernel.org> Date: Wed, 5 Aug 2026 14:26:22 +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 1/1] mm/ksm: avoid missing ksmd wakeups in ksm_enter To: Longlong Xia , akpm@linux-foundation.org Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, hugh.dickins@tiscali.co.uk, ieidus@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Longlong Xia References: <20260803152115.3479919-1-xialonglong2025@163.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/3/26 17:21, Longlong Xia wrote: > From: Longlong Xia > > __ksm_enter() decides whether ksmd needs a wakeup by checking if the > mm slot list is empty before inserting the new slot. > > The empty check is currently outside ksm_mmlist_lock. Another CPU can > remove the last slot and let ksmd go back to sleep after the unlocked > check, while this CPU inserts a new slot and skips the wakeup based on > the stale result. > > Take ksm_mmlist_lock before checking the list so the empty-to-nonempty > transition and the insertion are observed as one critical section. > > Fixes: 6e15838425ac ("ksm: keep quiet while list empty") > Signed-off-by: Longlong Xia > --- > mm/ksm.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 7d5b76478f0b..3f2f4707ca9e 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -3019,7 +3019,7 @@ int __ksm_enter(struct mm_struct *mm) > { > struct ksm_mm_slot *mm_slot; > struct mm_slot *slot; > - int needs_wakeup; > + bool needs_wakeup; Unrelated change that should not be included here. > > mm_slot = mm_slot_alloc(mm_slot_cache); > if (!mm_slot) > @@ -3027,10 +3027,9 @@ int __ksm_enter(struct mm_struct *mm) > > slot = &mm_slot->slot; > > + spin_lock(&ksm_mmlist_lock); > /* Check ksm_run too? Would need tighter locking */ > needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node); > - > - spin_lock(&ksm_mmlist_lock); > mm_slot_insert(mm_slots_hash, mm, slot); > /* > * When KSM_RUN_MERGE (or KSM_RUN_STOP), Makes sense to me. With the above variable change removed: Acked-by: David Hildenbrand (Arm) -- Cheers, David