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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XyTgdQWb; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 62144606A328 for ; Tue, 3 Nov 2026 16:08:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XyTgdQWb Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4DECD1F000C1; Tue, 3 Nov 2026 16:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793722115; bh=2UmsU380Tx/0AcknFjjF0B+jgdvRuMkPqh52dp469PY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XyTgdQWb9HCTddV1G3L44R58/3OaVtRDUWaTm0CzlSS5n3dfE0ttDE/QvABp3FcsB vtH5KDREUC6w7BI9UaeI4pnY0tNfWYXp5a8jpyPc7WeR2OTcy/YIybtY31beC564Yn w8eWzTCQTD+LBtoiI79mJN0Iq3gXd8R1rB02InO0eRmdjmpN9h6dFPLAb4JtEcu7Zm 4vUfLXXMrEIQYdALapFWis9EBtp1WuZqAvbS76Id5vK6MhYCbYU72XNCa2zUrzkLzy vFLdMRN/+22sIPqtdU91ENyfBAMs/erPyfh1PSBFnQK5RxgrknuyomCTyWpsp9fsCc 2TEtvGYKl9Slg== Message-ID: <1bf7784c-49ee-4f18-b1fb-205dc064f40f@kernel.org> Date: Tue, 3 Nov 2026 17:08:30 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] shmem: skip empty unmap ranges when punching holes To: Hungyu Lin , hughd@google.com Cc: baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261027171753.1485-1-dennylin0707@gmail.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 10/27/26 18:17, Hungyu Lin wrote: > When a hole ends within the first page, shmem_fallocate() calculates > unmap_end as -1. Casting it to u64 makes the range check succeed even > though the hole contains no complete pages. > > For example, punching one byte at offset zero calls unmap_mapping_range() > with a zero length, which means unmap to the end of the file. The file > contents are preserved outside the hole, but unrelated mappings are > removed and must fault back in. This can be reproduced with fallocate -p > -o 0 -l 1 on a mapped tmpfs file. > > Compare the exclusive rounded end against the rounded start to skip > empty ranges. Keep the unsigned comparison so rounding the start near > the maximum file offset continues to be handled correctly. > > Fixes: 83e4fa9c16e4 ("tmpfs: support fallocate FALLOC_FL_PUNCH_HOLE") I would pick this for the next merge window. Given that this issue is ... 14 years old I don't think we need to Cc stable. Other opinions? > Signed-off-by: Hungyu Lin > --- > mm/shmem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index d97fc32e7c94..08d5336c27a0 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -3864,7 +3864,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, > WRITE_ONCE(inode->i_private, &shmem_falloc); > spin_unlock(&inode->i_lock); > > - if ((u64)unmap_end > (u64)unmap_start) > + if ((u64)(unmap_end + 1) > (u64)unmap_start) Can this be >= ? > unmap_mapping_range(mapping, unmap_start, > 1 + unmap_end - unmap_start, 0); > shmem_truncate_range(inode, offset, offset + len - 1); -- Cheers, David