From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BCF9C249E5 for ; Wed, 4 Mar 2026 14:00:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772632851; cv=none; b=dAlmqNgxsy+basf2YcOF5I/qmgD89pavfWk7qjuzh4XRzxRO+KCEXkVhKKp9fxRYkaB4KCf44ZCWeoo0ZKD+C43ACca1rBG2iYTz1+sVreYqA245tMOB3WIi8kE9cyvxEFCSwwXElU+fBGPTD/m5x+eLS1YbjQi89lU1v2eYHKY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772632851; c=relaxed/simple; bh=iKD3YwaDmZBvntoN1UL5rht9ScDTUuy5/Ay84GFJXFk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qVirhQ5BxJc0oHLE0mo8ooN36iLqqM5Ld6zLWEptaVz94bLTsdUPKeH+QRdtVm0LZ7T34jTrLxZcgQYCWjSyfXBgbt8tNMn0kuwBxCPwtayr3Wtax/l05sY5THDTPdq5bvfJFBHY9YJhK8abYHCWdO46ni9uknCz/RqtiPrd6EE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bUwqURsS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bUwqURsS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB2AAC4AF09; Wed, 4 Mar 2026 14:00:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772632851; bh=iKD3YwaDmZBvntoN1UL5rht9ScDTUuy5/Ay84GFJXFk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bUwqURsShNUVzKeSU1D2X4VOfivUa3RtxubxcSSDYG+bdbbYJWE+Y4K7zaVj1Kcxi +fdOzBawT8AhsO4jJxT2buJ7iLkCUKiAzn/5ig7UwTvIunjupj85JMzs9iHZ6cKsRf h2jIQuBvoWltC74YmGMNdw5rJWksge7WQSBWFeO253Gz7cG8MAKc37mytzGa4IksUK 413oqzQoKpfJLRuEe0srdr5ssmZDtSg8dcVEN7/FKBcEBXewHpX0F1IoTvU7GQicqk VCDV76f0v5MZYJGC4YkLzkve7kF7AK+7nmevVYgthBr50syQzdVtC4PZE3PhAVnk8y YQKcGWzRlc6dw== Received: from phl-compute-06.internal (phl-compute-06.internal [10.202.2.46]) by mailfauth.phl.internal (Postfix) with ESMTP id DAE53F4006A; Wed, 4 Mar 2026 09:00:49 -0500 (EST) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-06.internal (MEProxy); Wed, 04 Mar 2026 09:00:49 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefgedrtddtgddvieefieeiucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepmfhirhihlhcu ufhhuhhtshgvmhgruhcuoehkrghssehkvghrnhgvlhdrohhrgheqnecuggftrfgrthhtvg hrnhepueeijeeiffekheeffffftdekleefleehhfefhfduheejhedvffeluedvudefgfek necuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepkhhirh hilhhlodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdduieduudeivdeiheeh qddvkeeggeegjedvkedqkhgrsheppehkvghrnhgvlhdrohhrghesshhhuhhtvghmohhvrd hnrghmvgdpnhgspghrtghpthhtohepfeekpdhmohguvgepshhmthhpohhuthdprhgtphht thhopehushgrmhgrrghrihhfieegvdesghhmrghilhdrtghomhdprhgtphhtthhopegrkh hpmheslhhinhhugidqfhhouhhnuggrthhiohhnrdhorhhgpdhrtghpthhtohepnhhprggt hhgvsehrvgguhhgrthdrtghomhdprhgtphhtthhopegurghvihgusehkvghrnhgvlhdroh hrghdprhgtphhtthhopeiiihihsehnvhhiughirgdrtghomhdprhgtphhtthhopehlihhn uhigqdhmmheskhhvrggtkhdrohhrghdprhgtphhtthhopehmrghtthhhvgifrdgsrhhosh htsehinhhtvghlrdgtohhmpdhrtghpthhtohepjhhoshhhuhgrrdhhrghhnhhjhiesghhm rghilhdrtghomhdprhgtphhtthhopehhrghnnhgvshestghmphigtghhghdrohhrgh X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 4 Mar 2026 09:00:47 -0500 (EST) Date: Wed, 4 Mar 2026 14:00:42 +0000 From: Kiryl Shutsemau To: Usama Arif Cc: Andrew Morton , npache@redhat.com, david@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, riel@surriel.com, shakeel.butt@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, Usama Arif Subject: Re: [PATCH] mm/migrate_device: fix folio refcount leak on folio_split_unmapped failure Message-ID: References: <20260304120132.3973445-1-usamaarif642@gmail.com> 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: <20260304120132.3973445-1-usamaarif642@gmail.com> On Wed, Mar 04, 2026 at 04:01:32AM -0800, Usama Arif wrote: > From: Usama Arif > > migrate_vma_split_unmapped_folio() takes an extra reference via > folio_get() before calling folio_split_unmapped(). On success, the > split consumes this reference: __folio_freeze_and_split_unmapped() > expects the +1 in its folio_ref_freeze() check, and distributes it > across the resulting sub-folios via folio_ref_unfreeze(...+1), which > are later balanced by folio_put() calls in __migrate_device_finalize(). Without this explanation folio_get() looks very random. And I still can't say I understand reference management for the folios here. Who takes reference for the folio if it !THP that gets return in the _finalize()? Can we get reference for THP and !THP at the same spot? I think we should avoid spacial-casing THP where possible. -- Kiryl Shutsemau / Kirill A. Shutemov