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Wen Yang 6d9e8c651d mm/page-writeback.c: avoid potential division by zero in wb_min_max_ratio() Patch series "use div64_ul() instead of div_u64() if the divisor is unsigned long". We were first inspired by commit `b0ab99e773` ("sched: Fix possible divide by zero in avg_atom () calculation"), then refer to the recently analyzed mm code, we found this suspicious place. 201 if (min) { 202 min *= this_bw; 203 do_div(min, tot_bw); 204 } And we also disassembled and confirmed it: /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 201 0xffffffff811c37da <__wb_calc_thresh+234>: xor %r10d,%r10d 0xffffffff811c37dd <__wb_calc_thresh+237>: test %rax,%rax 0xffffffff811c37e0 <__wb_calc_thresh+240>: je 0xffffffff811c3800 <__wb_calc_thresh+272> /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 202 0xffffffff811c37e2 <__wb_calc_thresh+242>: imul %r8,%rax /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 203 0xffffffff811c37e6 <__wb_calc_thresh+246>: mov %r9d,%r10d ---> truncates it to 32 bits here 0xffffffff811c37e9 <__wb_calc_thresh+249>: xor %edx,%edx 0xffffffff811c37eb <__wb_calc_thresh+251>: div %r10 0xffffffff811c37ee <__wb_calc_thresh+254>: imul %rbx,%rax 0xffffffff811c37f2 <__wb_calc_thresh+258>: shr $0x2,%rax 0xffffffff811c37f6 <__wb_calc_thresh+262>: mul %rcx 0xffffffff811c37f9 <__wb_calc_thresh+265>: shr $0x2,%rdx 0xffffffff811c37fd <__wb_calc_thresh+269>: mov %rdx,%r10 This series uses div64_ul() instead of div_u64() if the divisor is unsigned long, to avoid truncation to 32-bit on 64-bit platforms. This patch (of 3): The variables 'min' and 'max' are unsigned long and do_div truncates them to 32 bits, which means it can test non-zero and be truncated to zero for division. Fix this issue by using div64_ul() instead. Link: http://lkml.kernel.org/r/20200102081442.8273-2-wenyang@linux.alibaba.com Fixes: `693108a8a6` ("writeback: make bdi->min/max_ratio handling cgroup writeback aware") Signed-off-by: Wen Yang <wenyang@linux.alibaba.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Qian Cai <cai@lca.pw> Cc: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2020-01-13 18:19:02 -08:00
arch	RISC-V updates for v5.5-rc6	2020-01-12 16:48:39 -08:00
block	fs: move guard_bio_eod() after bio_set_op_attrs	2020-01-09 08:16:12 -07:00
certs	certs: Add wrapper function to check blacklisted binary hash	2019-11-12 12:25:50 +11:00
crypto	tpmdd fixes for Linux v5.5-rc3	2019-12-18 17:17:36 -08:00
Documentation	Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux	2020-01-11 15:40:43 -08:00
drivers	RISC-V updates for v5.5-rc6	2020-01-12 16:48:39 -08:00
fs	Char/Misc patch for 5.5-rc6	2020-01-10 13:25:24 -08:00
include	mm, debug_pagealloc: don't rely on static keys too early	2020-01-13 18:19:02 -08:00
init	mm, debug_pagealloc: don't rely on static keys too early	2020-01-13 18:19:02 -08:00
ipc	treewide: Use sizeof_field() macro	2019-12-09 10:36:44 -08:00
kernel	clone3-tls-v5.5-rc6	2020-01-11 15:33:48 -08:00
lib	Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2019-12-22 17:00:04 -08:00
LICENSES	LICENSES: Rename other to deprecated	2019-05-03 06:34:32 -06:00
mm	mm/page-writeback.c: avoid potential division by zero in wb_min_max_ratio()	2020-01-13 18:19:02 -08:00
net	tipc: fix wrong connect() return code	2020-01-08 15:57:35 -08:00
samples	samples/seccomp: Zero out members based on seccomp_notif_sizes	2020-01-02 13:03:39 -08:00
scripts	Kbuild fixes for v5.5 (2nd)	2020-01-03 11:21:25 -08:00
security	+ Bug fixes	2020-01-04 19:28:30 -08:00
sound	sound fixes for 5.5-rc6	2020-01-10 11:52:36 -08:00
tools	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2020-01-09 10:34:07 -08:00
usr	gen_initramfs_list.sh: fix 'bad variable name' error	2020-01-04 00:00:48 +09:00
virt	PPC KVM fix for 5.5	2019-12-22 13:18:15 +01:00
.clang-format	clang-format: Update with the latest for_each macro list	2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore	Opt out of scripts/get_maintainer.pl	2019-05-16 10:53:40 -07:00
.gitattributes	.gitattributes: use 'dts' diff driver for dts files	2019-12-04 19:44:11 -08:00
.gitignore	modpost: dump missing namespaces into a single modules.nsdeps file	2019-11-11 20:10:01 +09:00
.mailmap	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2019-12-22 09:54:33 -08:00
COPYING
CREDITS	Linux 5.4-rc4	2019-10-29 04:43:29 -06:00
Kbuild	kbuild: do not descend to ./Kbuild when cleaning	2019-08-21 21:03:58 +09:00
Kconfig	docs: kbuild: convert docs to ReST and rename to *.rst	2019-06-14 14:21:21 -06:00
MAINTAINERS	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2020-01-09 10:34:07 -08:00
Makefile	Linux 5.5-rc6	2020-01-12 16:55:08 -08:00
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.