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Linus Torvalds 6cd06ab12d gup: make the stack expansion warning a bit more targeted 
I added a warning about about GUP no longer expanding the stack in
commit a425ac5365 ("gup: add warning if some caller would seem to want
stack expansion"), but didn't really expect anybody to hit it.

And it's true that nobody seems to have hit a _real_ case yet, but we
certainly have a number of reports of false positives.  Which not only
causes extra noise in itself, but might also end up hiding any real
cases if they do exist.

So let's tighten up the warning condition, and replace the simplistic

	vma = find_vma(mm, start);
	if (vma && (start < vma->vm_start)) {
		WARN_ON_ONCE(vma->vm_flags & VM_GROWSDOWN);

with a

	vma = gup_vma_lookup(mm, start);

helper function which works otherwise like just "vma_lookup()", but with
some heuristics for when to warn about gup no longer causing stack
expansion.

In particular, don't just warn for "below the stack", but warn if it's
_just_ below the stack (with "just below" arbitrarily defined as 64kB,
because why not?).  And rate-limit it to at most once per hour, which
means that any false positives shouldn't completely hide subsequent
reports, but we won't be flooding the logs about it either.

The previous code triggered when some GUP user (chromium crashpad)
accessing past the end of the previous vma, for example.  That has never
expanded the stack, it just causes GUP to return early, and as such we
shouldn't be warning about it.

This is still going trigger the randomized testers, but to mitigate the
noise from that, use "dump_stack()" instead of "WARN_ON_ONCE()" to get
the kernel call chain.  We'll get the relevant information, but syzbot
shouldn't get too upset about it.

Also, don't even bother with the GROWSUP case, which would be using
different heuristics entirely, but only happens on parisc.

Reported-by: kernel test robot <oliver.sang@intel.com>
Reported-by: John Hubbard <jhubbard@nvidia.com>
Reported-by: syzbot+6cf44e127903fdf9d929@syzkaller.appspotmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2023-07-05 09:33:31 -07:00
arch Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
block block-6.5-2023-07-03 2023-07-03 18:48:38 -07:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto This update includes the following changes: 2023-06-30 21:27:13 -07:00
Documentation More power management updates for 6.5-rc1 2023-07-04 11:22:50 -07:00
drivers Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
fs afs: Fix accidental truncation when storing data 2023-07-04 12:24:32 -07:00
include Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
init Kbuild updates for v6.5 2023-07-01 09:24:31 -07:00
io_uring io_uring-6.5-2023-07-03 2023-07-03 18:43:10 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel module: fix init_module_from_file() error handling 2023-07-04 10:17:11 -07:00
lib Char/Misc and other driver subsystem updates for 6.5-rc1 2023-07-03 12:46:47 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm gup: make the stack expansion warning a bit more targeted 2023-07-05 09:33:31 -07:00
net - New Drivers 2023-07-03 11:26:05 -07:00
rust rust: error: impl Debug for Error with errname() integration 2023-06-13 01:24:42 +02:00
samples Char/Misc and other driver subsystem updates for 6.5-rc1 2023-07-03 12:46:47 -07:00
scripts Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
security Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
sound ARM: SoC changes for 6.5 2023-06-29 15:28:33 -07:00
tools virtio: features, fixes, cleanups 2023-07-03 15:38:26 -07:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM64: 2023-07-03 15:32:22 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Revert ".gitignore: ignore *.cover and *.mbx" 2023-07-04 15:05:12 -07:00
.mailmap - New Drivers 2023-07-03 10:55:04 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS - Address -Wmissing-prototype warnings 2023-06-26 16:43:54 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS power supply and reset changes for the 6.5 series 2023-07-03 17:23:16 -07:00
Makefile Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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 Restructured Text 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.