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b=fnrpq6fXUrx9QXPgz+DBX+Qxzr/8ycksAoTg+LwWybP0PSZk4FDpF6DgEmo2LweQ+ 9WRQNo+wYjPVEW84HwBUh6/j2fQvPZS1eYLtOuhesU/AlAoH9rCpA5u8O7ZN723wzg 17RfltwDDU/LSt1+oAQljK15ipIKPcAWW9sSBlmt9LqlYSFx1yvFd5rHpqU6m+GBo0 kRAAr9s8jITykV8Yvg2yjJze7/OSoExQCYaiTXAvO2qlXly5L1oNXj6uM0TmXpX4y/ z4M0z8J9H5dkjewW9/VPnD4ib9jTFsbBfXNvgGsHvJ+Lk95kBH6wLcxwB4k4R6OfAq dV5bTMLRSo6Gg== Date: Sun, 23 Nov 2025 16:16:19 +0200 From: Mike Rapoport To: Pasha Tatashin Cc: pratyush@kernel.org, jasonmiu@google.com, graf@amazon.com, dmatlack@google.com, rientjes@google.com, corbet@lwn.net, rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com, kanie@linux.alibaba.com, ojeda@kernel.org, aliceryhl@google.com, masahiroy@kernel.org, akpm@linux-foundation.org, tj@kernel.org, yoann.congal@smile.fr, mmaurer@google.com, roman.gushchin@linux.dev, chenridong@huawei.com, axboe@kernel.dk, mark.rutland@arm.com, jannh@google.com, vincent.guittot@linaro.org, hannes@cmpxchg.org, dan.j.williams@intel.com, david@redhat.com, joel.granados@kernel.org, rostedt@goodmis.org, anna.schumaker@oracle.com, song@kernel.org, linux@weissschuh.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rafael@kernel.org, dakr@kernel.org, bartosz.golaszewski@linaro.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com, yesanishhere@gmail.com, Jonathan.Cameron@huawei.com, quic_zijuhu@quicinc.com, aleksander.lobakin@intel.com, ira.weiny@intel.com, andriy.shevchenko@linux.intel.com, leon@kernel.org, lukas@wunner.de, bhelgaas@google.com, wagi@kernel.org, djeffery@redhat.com, stuart.w.hayes@gmail.com, ptyadav@amazon.de, lennart@poettering.net, brauner@kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, saeedm@nvidia.com, ajayachandra@nvidia.com, jgg@nvidia.com, parav@nvidia.com, leonro@nvidia.com, witu@nvidia.com, hughd@google.com, skhawaja@google.com, chrisl@kernel.org Subject: Re: [PATCH v7 04/22] liveupdate: luo_session: add sessions support Message-ID: References: <20251122222351.1059049-1-pasha.tatashin@soleen.com> <20251122222351.1059049-5-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251122222351.1059049-5-pasha.tatashin@soleen.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 920B4C0015 X-Stat-Signature: awdkoyswcuw7fedkcgifjukb37oq9epi X-HE-Tag: 1763907405-479129 X-HE-Meta: U2FsdGVkX19hm+4qyL9fgmWn82zBjFQTOLCEfkX6Ep2UU0iFMfVz0sargSc40fmmp6Kp6IcxG2mFwK6jylRHdX/en600KhBOh45wse0xzMrNxHPLlx3Xgfhq0iNtSNpNxHu0IpnlBwJxgHgFnVUajvilqQ0gvT9LRZMSqyKOhZvxA5h5qTJclNiWB3c/2ysePRElsRsL17/GG7T1u/Lovnbpyet78RMPRVQFTNx1KU1iYKqnQx0Kkm75YuWsXz2wAsVdBo9xo+eWV2DRmW1rl8nDes1iW9Yo7H+Qw83ZL5jw6eHSCMEBhSFv/EGMrxrMgGT/GWxsIFPI1xZx28lhKmBO1E3DEqcN1k/ocdoBDMQTaQeTkZyiJDFb5eTxIrhfXg7fryiresfFGS20G8UIBTTo/GbzlvgkafshyX/6yfkB1GoPs9/oHK0/xeUuWi1DdPJMwhs/qSyOTXQjjUeDuAlDt7px+QNtOTSwHdGKiLqHONImKFnqr4hwm+bVJdXzGbGs5i6aGyFGeUFWCBSv7uSVOR4TQia6DViab6G52q7rXoHK2HphMBJsmVcPpQ8dZkLGHHSrDsjWB3xon24yX0J2HpExTJrhppuQeOKQv3clyMeIiBbPmmCcUHnG0R37YKVo9Dmof+lWZ4ikqWeNVEA5+Wp+TxNWjWEwcHbgkrOlf7zS0ghfdHhWYPwAyNSD1U0yjO6zJWjVeB9yG0wqRsU8g9UowOp2FpdqiIjoOypdDmLN4V3q3XuFziyfITOgklv10uZ9qj8nvdoM6p4OhS2MvmjGaBSrervXFdJxm7GfRAAFHS/juBifTvD2S2b+3UhHG18peW6rdY/JCNqsLoigWfjXtMYN1bB9HFOMzaDJx4fLdyYAoqwZqpOVhOUOyoAPRFnxtp0vfaBxkhXuOB6Y0JtUSXwaWkERhUY8SaMIKzGX4fa7LUAYfeLrcw2lgWuPLzDlW4RcMiO4Sjf tl0k6YuV O5lLmE/FuyUrDp9yVuxHmxb0SlPjuVb+Xp5w8TwlQ1H81md0S2qDre/mkw27HDIXbFFYq8DJ8oGeNpVeqGMUgwfGAcfoJYqE5OWRKg/Vd61BAzIXkiQj3kdgTXpyUA7r8cNQsEmy8wDAxYBsoKtptPh50x4Oy2C/zzAZoQfMBCT2eka89kjzC+R1Ts2snHkIBkBkvdOBPgE9f7fvb2+eVDibFNWwpKLPz05BjBx8J8k+uDE8sf8YRv4PFJQ8szBDBJg1U11DwM35Nh1HtHgMbVuAbXGlKbtc+mpXs7ORNJBCJ3LF84P4EDiYVaCL+hq59HvmIrd5+qjsPzCABJbrFMCkQ/2y0HnNDUjt1RxLNOsFpV+k1AYfQ/6Jii5fuRo9kB7af9jjDiP4DDdCPspqn+kOJYztdRUQBe/zNpEJeb+1JojybnMCirB3sRs8WOqX2SG0QrbjFpku1YNg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Nov 22, 2025 at 05:23:31PM -0500, Pasha Tatashin wrote: > Introduce concept of "Live Update Sessions" within the LUO framework. > LUO sessions provide a mechanism to group and manage `struct file *` > instances (representing file descriptors) that need to be preserved > across a kexec-based live update. > > Each session is identified by a unique name and acts as a container > for file objects whose state is critical to a userspace workload, such > as a virtual machine or a high-performance database, aiming to maintain > their functionality across a kernel transition. > > This groundwork establishes the framework for preserving file-backed > state across kernel updates, with the actual file data preservation > mechanisms to be implemented in subsequent patches. > > Signed-off-by: Pasha Tatashin > --- > include/linux/kho/abi/luo.h | 71 +++++ > include/uapi/linux/liveupdate.h | 3 + > kernel/liveupdate/Makefile | 3 +- > kernel/liveupdate/luo_core.c | 9 + > kernel/liveupdate/luo_internal.h | 29 ++ > kernel/liveupdate/luo_session.c | 462 +++++++++++++++++++++++++++++++ > 6 files changed, 576 insertions(+), 1 deletion(-) > create mode 100644 kernel/liveupdate/luo_session.c > ... > +int __init luo_session_setup_outgoing(void *fdt_out) > +{ > + struct luo_session_header_ser *header_ser; > + void *outgoing_buffer; > + u64 header_ser_pa; > + int err; > + > + outgoing_buffer = kho_alloc_preserve(LUO_SESSION_PGCNT << PAGE_SHIFT); > + if (IS_ERR(outgoing_buffer)) > + return PTR_ERR(header_ser); Should be return PTR_ERR(outgoing_buffer); Or, preferably, just drop outgoing_buffer and use header_ser everywhere. > + header_ser = outgoing_buffer; > + header_ser_pa = virt_to_phys(header_ser); > + > + err = fdt_begin_node(fdt_out, LUO_FDT_SESSION_NODE_NAME); > + err |= fdt_property_string(fdt_out, "compatible", > + LUO_FDT_SESSION_COMPATIBLE); > + err |= fdt_property(fdt_out, LUO_FDT_SESSION_HEADER, &header_ser_pa, > + sizeof(header_ser_pa)); > + err |= fdt_end_node(fdt_out); > + > + if (err) > + goto err_unpreserve; > + > + luo_session_global.outgoing.header_ser = header_ser; > + luo_session_global.outgoing.ser = (void *)(header_ser + 1); > + luo_session_global.outgoing.active = true; > + > + return 0; > + > +err_unpreserve: > + kho_unpreserve_free(header_ser); > + return err; > +} ... > +int luo_session_deserialize(void) > +{ > + struct luo_session_header *sh = &luo_session_global.incoming; > + static bool is_deserialized; > + static int err; > + > + /* If has been deserialized, always return the same error code */ > + if (is_deserialized) > + return err; is_deserialized and err are uninitialized here. > + > + is_deserialized = true; > + if (!sh->active) > + return 0; > + ... > +/** > + * luo_session_quiesce - Ensure no active sessions exist and lock session lists. > + * > + * Acquires exclusive write locks on both incoming and outgoing session lists. > + * It then validates no sessions exist in either list. > + * > + * This mechanism is used during file handler un/registration to ensure that no > + * sessions are currently using the handler, and no new sessions can be created > + * while un/registration is in progress. It makes sense to add something like this comment from luo_file.c here as well: * This prevents registering new handlers while sessions are active or * while deserialization is in progress. > + * > + * Return: > + * true - System is quiescent (0 sessions) and locked. > + * false - Active sessions exist. The locks are released internally. > + */ With those addressed: Reviewed-by: Mike Rapoport (Microsoft) -- Sincerely yours, Mike.