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Paul Burton 133d68e0ed MIPS: Fix cmpxchg on 32b signed ints for 64b kernel with !kernel_uses_llsc 
Commit 8263db4d77 ("MIPS: cmpxchg: Implement __cmpxchg() as a
function") refactored our implementation of __cmpxchg() to be a function
rather than a macro, with the aim of making it easier to read & modify.
Unfortunately the commit breaks use of cmpxchg() for signed 32 bit
values when we have a 64 bit kernel with kernel_uses_llsc == false,
because:

 - In cmpxchg_local() we cast the old value to the type the pointer
   points to, and then to an unsigned long. If the pointer points to a
   signed type smaller than 64 bits then the old value will be sign
   extended to 64 bits. That is, bits beyond the size of the pointed to
   type will be set to 1 if the old value is negative. In the case of a
   signed 32 bit integer with a negative value, bits 63:32 will all be
   set.

 - In __cmpxchg_asm() we load the value from memory, ie. dereference the
   pointer, and store the value as an unsigned integer (__ret) whose
   size matches the pointer. For a 32 bit cmpxchg() this means we store
   the value in a u32, because the pointer provided to __cmpxchg_asm()
   by __cmpxchg() is of type volatile u32 *.

 - __cmpxchg_asm() then checks whether the value in memory (__ret)
   matches the provided old value, by comparing the two values. This
   results in the u32 being promoted to a 64 bit unsigned long to match
   the old argument - however because both types are unsigned the value
   is zero extended, which does not match the sign extension performed
   on the old value in cmpxchg_local() earlier.

This mismatch means that unfortunate cmpxchg() calls can incorrectly
fail for 64 bit kernels with kernel_uses_llsc == false. This is the case
on at least non-SMP Cavium Octeon kernels, which hardcode
kernel_uses_llsc in their cpu-feature-overrides.h header. Using a
v4.13-rc7 kernel configured using cavium_octeon_defconfig with SMP
manually disabled, this presents itself as oddity when we reach
userland - for example:

  can't run '/bin/mount': Text file busy
  can't run '/bin/mkdir': Text file busy
  can't run '/bin/mkdir': Text file busy
  can't run '/bin/mount': Text file busy
  can't run '/bin/hostname': Text file busy
  can't run '/etc/init.d/rcS': Text file busy
  can't run '/sbin/getty': Text file busy
  can't run '/sbin/getty': Text file busy

It appears that some part of the init process, which is in this case
buildroot's busybox init, is running successfully. It never manages to
reach the login prompt though, and complains about /sbin/getty being
busy repeatedly and indefinitely.

Fix this by casting the old value provided to __cmpxchg_asm() to an
appropriately sized unsigned integer, such that we consistently
zero-extend avoiding the mismatch. The __cmpxchg_small() case for 8 & 16
bit values is unaffected because __cmpxchg_small() already masks
provided values appropriately.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: 8263db4d77 ("MIPS: cmpxchg: Implement __cmpxchg() as a function")
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17226/
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2017-10-09 16:31:32 +02:00
arch MIPS: Fix cmpxchg on 32b signed ints for 64b kernel with !kernel_uses_llsc 2017-10-09 16:31:32 +02:00
block bsg-lib: fix use-after-free under memory-pressure 2017-10-04 08:35:04 -06:00
certs modsign: add markers to endif-statements in certs/Makefile 2017-07-14 11:01:37 +10:00
crypto crypto: af_alg - update correct dst SGL entry 2017-09-20 17:42:42 +08:00
Documentation Merge branch 'i2c/for-current-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2017-10-07 10:07:51 -07:00
drivers SCSI fixes on 20171007 2017-10-07 12:34:16 -07:00
firmware firmware: Restore support for built-in firmware 2017-09-16 10:58:48 -07:00
fs Changes since last update: 2017-10-06 15:53:36 -07:00
include SCSI fixes on 20171007 2017-10-07 12:34:16 -07:00
init Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-09-14 18:54:01 -07:00
ipc fix a typo in put_compat_shm_info() 2017-09-25 20:41:46 -04:00
kernel Merge branch 'core-watchdog-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-06 08:36:41 -07:00
lib lib/ratelimit.c: use deferred printk() version 2017-10-03 17:54:26 -07:00
mm mm/memory_hotplug: define find_{smallest|biggest}_section_pfn as unsigned long 2017-10-03 17:54:26 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-05 08:40:09 -07:00
samples media updates for v4.14-rc1 2017-09-07 12:53:14 -07:00
scripts checkpatch: fix ignoring cover-letter logic 2017-10-03 17:54:26 -07:00
security lsm: fix smack_inode_removexattr and xattr_getsecurity memleak 2017-10-04 18:03:15 +11:00
sound sound fixes for 4.14-rc4 2017-10-05 10:39:29 -07:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-01 12:06:31 -07:00
usr ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk. 2017-07-06 16:24:30 -07:00
virt Revert "KVM: Don't accept obviously wrong gsi values via KVM_IRQFD" 2017-09-19 08:37:17 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap Update James Hogan's email address 2017-10-04 17:11:53 -07:00
COPYING
CREDITS selinux/stable-4.14 PR 20170831 2017-09-12 13:21:00 -07:00
Kbuild kbuild: Consolidate header generation from ASM offset information 2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS ARC udpates for 4.14-rc4 2017-10-06 15:57:08 -07:00
Makefile Linux 4.14-rc4 2017-10-08 20:53:29 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.