mirror of
https://github.com/torvalds/linux.git
synced 2026-09-24 20:19:22 -04:00
1096bc93df
The code wasn't exactly wrong, but it was very odd, and it used FOLL_FORCE together with FOLL_WRITE when it really didn't need to (it only set FOLL_WRITE for writable mappings, so then the FOLL_FORCE was pointless). It also pointlessly called __get_user_pages() even when it knew it wouldn't populate anything because the vma wasn't accessible and it explicitly tested for and did *not* set FOLL_FORCE for inaccessible vma's. This code does need to use FOLL_FORCE, because we want to do fault in writable shared mappings, but then the mapping may not actually be readable. And we don't want to use FOLL_WRITE (which would match the permission of the vma), because that would also dirty the pages, which we don't want to do. For very similar reasons, FOLL_FORCE populates a executable-only mapping with no read permissions. We don't have a FOLL_EXEC flag. Yes, it would probably be cleaner to split FOLL_WRITE into two bits (for separate permission and dirty bit handling), and add a FOLL_EXEC flag for the "GUP executable page" case. That would allow us to avoid FOLL_FORCE entirely here. But that's not how our FOLL_xyz bits have traditionally worked, and that would be a much bigger patch. So this at least avoids the FOLL_FORCE | FOLL_WRITE combination that made one of my experimental validation patches trigger a warning. That warning was a false positive (and my experimental patch was incomplete anyway), but it all made me look at this and decide to clean at least this small case up. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.