Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode
Christian Brauner <[email protected]>
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| Message-ID | <20230929-keimt-umspannen-bfd12d2c2033@brauner> |
On Thu, Sep 28, 2023 at 10:41:34AM -0700, Linus Torvalds wrote: > On Thu, 28 Sept 2023 at 04:06, Jeff Layton <[email protected]> wrote: > > > > Move i_blocks up above the i_lock, which moves the new 4 byte hole to > > just after the timestamps, without changing the size of the structure. > > I'm sure others have mentioned this, but 'struct inode' is marked with > __randomize_layout, so the actual layout may end up being very > different. > > I'm personally not convinced the whole structure randomization is > worth it - it's easy enough to figure out for any distro kernel since > the seed has to be the same across machines for modules to work, so > even if the seed isn't "public", any layout is bound to be fairly > easily discoverable. > > So the whole randomization only really works for private kernel > builds, and it adds this kind of pain where "optimizing" the structure > layout is kind of pointless depending on various options. > > I certainly *hope* no distro enables that pointless thing, but it's a worry. They don't last we checked. Just last cycle we moved stuff in struct file around to optimize things and we explicitly said we don't give a damn about struct randomization. Anyone who enables this will bleed performance pretty badly, I would reckon.