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b=k8qOsmK0MFixaOE+ur9RDYKjJNzgQETCBx4Oa3wWC/9H1PoxgtrNQNX7/5A4GpW/U v0JV7rkpnvyJL1rYx6chzjbZgoupm4vdk57fliNPi39btz2xk1F5FCee4m+Rr8Cqe1 E9l6XiQcA2IWOIwOMkCEhjEqnPIJml2n1VV2Eze/Ydq0SxT4eVjeex+rOaqjxgNVxe 53QRcV94fUWhBLEk/49eJ3jbINePYq/OtvXRBht1s5jNKnMBp3RxBxQ8lxoVUsjDPB tQkNIka36Z6rQKVe/hymFXQ83s2NhHD4on6LZ3syqdlujrr7+PFw2Mcordkbsq1LyH /sCwFTOTSrNUQ== Date: Sun, 23 Nov 2025 17:29:09 +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 11/22] mm: shmem: allow freezing inode mapping Message-ID: References: <20251122222351.1059049-1-pasha.tatashin@soleen.com> <20251122222351.1059049-12-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251122222351.1059049-12-pasha.tatashin@soleen.com> X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 3F22CC000C X-Stat-Signature: bpenj9jwuud97an7dppthhib9ki7oemj X-HE-Tag: 1763911776-655669 X-HE-Meta: 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 fH+E70M5 eljbsvUgsKIdbJNaeG28rKZwpZT7CNhAirC9VxeApYsHpXG1KTHSUuQigSp2o7vQZu3iPweHtrmauhu4GiOVUQQczO85CFA2l+3puZOeDOH75GkEDtsDz5e7grIWPL43JSuchonkwzHnekcNuUYB/iibPo69JdYh/Y9lTp7FF60boBnbH03EQTijyUCcygDUJ5dVmG2F5RCgCvOSqJDXKsNDJ3Z1QfILPqcPfNdDnD+lyolksyMdf6ktJojz24p7nCoAHrXrmtWIzOj3pSup/ZYVu2g+B87XDHrIvLdOl4p+dmS2RbeoJMmAg939GecDRuFqBCJYXKhTIshOIdbl12EO7nm4ZwHEX9RWXv0Ti/QTnoXBLpfrhSSv10+ole7aLnpQPg4MxX54T+GWXfuyR9D+ZwQ== 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 05:23:38PM -0500, Pasha Tatashin wrote: > From: Pratyush Yadav > > To prepare a shmem inode for live update, its index -> folio mappings > must be serialized. Once the mappings are serialized, they cannot change > since it would cause the serialized data to become inconsistent. This > can be done by pinning the folios to avoid migration, and by making sure > no folios can be added to or removed from the inode. > > While mechanisms to pin folios already exist, the only way to stop > folios being added or removed are the grow and shrink file seals. But > file seals come with their own semantics, one of which is that they > can't be removed. This doesn't work with liveupdate since it can be > cancelled or error out, which would need the seals to be removed and the > file's normal functionality to be restored. > > Introduce SHMEM_F_MAPPING_FROZEN to indicate this instead. It is > internal to shmem and is not directly exposed to userspace. It functions > similar to F_SEAL_GROW | F_SEAL_SHRINK, but additionally disallows hole > punching, and can be removed. > > Signed-off-by: Pratyush Yadav > Signed-off-by: Pasha Tatashin > --- > include/linux/shmem_fs.h | 17 +++++++++++++++++ > mm/shmem.c | 19 ++++++++++++++++--- > 2 files changed, 33 insertions(+), 3 deletions(-) > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > index 650874b400b5..d34a64eafe60 100644 > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h > @@ -24,6 +24,14 @@ struct swap_iocb; > #define SHMEM_F_NORESERVE BIT(0) > /* Disallow swapping. */ > #define SHMEM_F_LOCKED BIT(1) > +/* > + * Disallow growing, shrinking, or hole punching in the inode. Combined with > + * folio pinning, makes sure the inode's mapping stays fixed. > + * > + * In some ways similar to F_SEAL_GROW | F_SEAL_SHRINK, but can be removed and > + * isn't directly visible to userspace. > + */ > +#define SHMEM_F_MAPPING_FROZEN BIT(2) > > struct shmem_inode_info { > spinlock_t lock; > @@ -186,6 +194,15 @@ static inline bool shmem_file(struct file *file) > return shmem_mapping(file->f_mapping); > } > > +/* Must be called with inode lock taken exclusive. */ > +static inline void shmem_freeze(struct inode *inode, bool freeze) > +{ > + if (freeze) > + SHMEM_I(inode)->flags |= SHMEM_F_MAPPING_FROZEN; > + else > + SHMEM_I(inode)->flags &= ~SHMEM_F_MAPPING_FROZEN; > +} > + > /* > * If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages > * beyond i_size's notion of EOF, which fallocate has committed to reserving: > diff --git a/mm/shmem.c b/mm/shmem.c > index 1d5036dec08a..cb74a5d202ac 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1292,9 +1292,13 @@ static int shmem_setattr(struct mnt_idmap *idmap, > loff_t newsize = attr->ia_size; > > /* protected by i_rwsem */ > - if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) || > - (newsize > oldsize && (info->seals & F_SEAL_GROW))) > - return -EPERM; > + if (newsize != oldsize) { > + if (info->flags & SHMEM_F_MAPPING_FROZEN) > + return -EPERM; > + if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) || > + (newsize > oldsize && (info->seals & F_SEAL_GROW))) > + return -EPERM; > + } > > if (newsize != oldsize) { I'd stick if (info->flags & SHMEM_F_MAPPING_FROZEN) return -EPERM; here and leave the seals check alone. Other than than Reviewed-by: Mike Rapoport (Microsoft) -- Sincerely yours, Mike.