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AJvYcCUADG+QqnwZNx+Ne6SKsDDYOd69eqaKNiyGPGMjs6n5sY9SIuctkG/NDukJUNZcT/9sgNirKQq4sA==@kvack.org X-Gm-Message-State: AOJu0Yw4iRF+h28OxzjeQRgXsm047SOolapvIDmLdJ5PCaKzf54Bwpk4 QkFXHHQAmjPjgz8YTiFWB3sqMTuU6NzCOHmCGJ7k38DmS8uOPnRNceK9NY1o5IYOeEWTCxiV0kr gyXkB2y3cRRtRWN2Mi8Sq/vC5Kd6rk+Ty3Zk7utI5HQ== X-Gm-Gg: ATEYQzxNL4AxQkpiWFy4sB71bZDfqAhpu1N7VuuBkrVvigSHMoqtqkTSqKB0QenQoVm fTzaLdwMsEcSnfQelLMf4L8flXmJjQedD00KP0m/4n+jp6XPWY751IL/bpr4+TlOOEzOiCUxsen vg5UXJJltb7loQuh5C1amgX0BUolY3P5fqPEBP1H7uLqkRC2pdjpJjQSNYB5j8AMyuXuENrlHZE FuGHYxnmRW/ZL1/gyWI3UrCpLZduMDVjXansjZY/6qZ7JMHfBT9UYDd9vyo5p4cFsOJ2r4ICYny 7xPZY5l3rEwWyha3jsX7aPrg+OkXoYOfzJsWyg== X-Received: by 2002:a05:6402:4582:b0:66a:3948:d038 with SMTP id 4fb4d7f45d1cf-66a826e4411mr904611a12.19.1774406991473; Tue, 24 Mar 2026 19:49:51 -0700 (PDT) MIME-Version: 1.0 References: <20260318141637.1870220-10-pasha.tatashin@soleen.com> <20260318141637.1870220-13-pasha.tatashin@soleen.com> In-Reply-To: From: Pasha Tatashin Date: Tue, 24 Mar 2026 22:49:14 -0400 X-Gm-Features: AQROBzC0DwhMMWi0EsUVCJug7-pyk_Y26naXj4MKTWNsdNop8tv0j-A6EbSiOVU Message-ID: Subject: Re: [PATCH v2 3/8] liveupdate: Remove file handler module refcounting To: David Matlack Cc: rppt@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, pratyush@kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 3465A180006 X-Stat-Signature: o3wn11kajwsczj5x5f7bb8fzt1wru8a3 X-HE-Tag: 1774406992-80015 X-HE-Meta: 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 uKXt41Pi ND8gRoUiYSOo+Ifn/aDrTm+F5vd6v2F8aYG+u5HRmelt/iiKhxtisI8NInQfcAJfFQHBlvJVBNwjidHr2gF4qonKI/9I0FXQ7EaCW8t6wLHjFIckF8kGyX7roLyR1ndrFl1Iga+5WipngvbPnOyxhex4ReXOS2TVVTi6AgLnUcjpVEazuMa901zpD1hFhNWqKdGlaw7+WOEzb1pGpv68RtQ09qziH22n6NFT8V24SmQSSY7Vpl07r0GLL4th3fRC8AhhP3I6TufQFlNgSDsQVcSFFwY7Efa36jf7m/mplSQN7kHZQ7VaINc8SAg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 5:24=E2=80=AFPM David Matlack = wrote: > > On Wed, Mar 18, 2026 at 7:17=E2=80=AFAM Pasha Tatashin > wrote: > > > > File handlers do not need to pin modules indefinitely or during active > > live update sessions. The VFS 'struct file' pins the file handler's mod= ule > > via f_op->owner during active sessions, making dynamic reference counti= ng > > unnecessary for handlers. > > > > When a file is preserved, the live update core obtains a 'struct file' > > via fdget(). As long as the file is kept open within the live update > > session, the module is pinned by the VFS and cannot be unloaded. > > After invoking the file handler's retrieve(), LUO should probably > check that the created file's owner matches the file handler's owner, > since this scheme relies on that being true. > > If there is a mismatch, LUO can put the file that was just created, > log a warning, and return an error up to the user. Is there a reason why taking a file handler module reference is problematic for vfio or iommu? Could we take it while files are present in incoming or outgoing sessions? Overall, it is because it cover corener cases such as if the file struct owner is the same as LUO file handler and also this approach covers the deserialziation side nicely. Pasha