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Fri, 20 Mar 2026 07:27:56 -0700 (PDT) MIME-Version: 1.0 References: <20260317023834.487682-1-pasha.tatashin@soleen.com> In-Reply-To: From: Pasha Tatashin Date: Fri, 20 Mar 2026 10:27:19 -0400 X-Gm-Features: AaiRm53KwLS0dZ_0F2E6R9Ka7xHwPaNadXUdllrLPjUjJCiW_fFG9VxgEmZKncE Message-ID: Subject: Re: [RFC] liveupdate: prevent double preservation To: Jan Kara Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, rppt@kernel.org, pratyush@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 37152C0004 X-Stat-Signature: wj3x856xdzkypowf87qbqbrskq337jw7 X-Rspam-User: X-HE-Tag: 1774016877-751941 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 20, 2026 at 9:47=E2=80=AFAM Jan Kara wrote: > > On Mon 16-03-26 22:38:34, Pasha Tatashin wrote: > > Currently, LUO does not prevent the same file from being preserved twic= e > > across different active sessions. > > > > Add a new i_state flag I_LUO_PRESERVED and update luo_preserve_file() > > to check and set this flag when a file is preserved, and clear it in > > luo_file_unpreserve_files() when it is released. This ensures that the > > same file (inode) cannot be preserved by multiple sessions. If another > > session attempts to preserve an already preserved file, it will now > > fail with -EBUSY. > > > > Signed-off-by: Pasha Tatashin > > --- > > > > Background: > > Because LUO preserves files of absolutely different types: memfd, and > > upcoming vfiofd [1], iommufd [2], guestmefd (and possible kvmfd/cpufd)= . > > There is no common private data or guarantee on how to prevent that the > > same file is not preserved twice beside using inode or some slower and > > expensive method like hashtables. > > OK, I guess since this is a single bit, we can live with that although it > seems a bit wrong that LUO needs this in generic struct inode. But all > other "cleaner" variants I could think of were just an overkill. So feel > free to add: > > Acked-by: Jan Kara > > Just one nit below: > > > [1] https://lore.kernel.org/all/20260129212510.967611-1-dmatlack@google= .com > > [2] https://lore.kernel.org/all/20260203220948.2176157-1-skhawaja@googl= e.com > > > > @@ -744,7 +746,8 @@ enum inode_state_flags_enum { > > I_CREATING =3D (1U << 15), > > I_DONTCACHE =3D (1U << 16), > > I_SYNC_QUEUED =3D (1U << 17), > > - I_PINNING_NETFS_WB =3D (1U << 18) > > + I_PINNING_NETFS_WB =3D (1U << 18), > > + I_LUO_PRESERVED =3D (1U << 19) > > Add comma at the end of line here please so that we don't have to modify > the last line again. Will do. Thank you, Pasha > > Honza > > -- > Jan Kara > SUSE Labs, CR