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Tejun Heo edaa26334c iocost: Fix divide-by-zero on donation from low hweight cgroup 
The donation calculation logic assumes that the donor has non-zero
after-donation hweight, so the lowest active hweight a donating cgroup can
have is 2 so that it can donate 1 while keeping the other 1 for itself.
Earlier, we only donated from cgroups with sizable surpluses so this
condition was always true. However, with the precise donation algorithm
implemented, f1de2439ec ("blk-iocost: revamp donation amount
determination") made the donation amount calculation exact enabling even low
hweight cgroups to donate.

This means that in rare occasions, a cgroup with active hweight of 1 can
enter donation calculation triggering the following warning and then a
divide-by-zero oops.

 WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928 transfer_surpluses.cold+0x0/0x53 [884/94867]
 ...
 RIP: 0010:transfer_surpluses.cold+0x0/0x53
 Code: 92 ff 48 c7 c7 28 d1 ab b5 65 48 8b 34 25 00 ae 01 00 48 81 c6 90 06 00 00 e8 8b 3f fe ff 48 c7 c0 ea ff ff ff e9 95 ff 92 ff <0f> 0b 48 c7 c7 30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0
4
 ...
 Call Trace:
  <IRQ>
  ioc_timer_fn+0x1043/0x1390
  call_timer_fn+0xa1/0x2c0
  __run_timers.part.0+0x1ec/0x2e0
  run_timer_softirq+0x35/0x70
 ...
 iocg: invalid donation weights in /a/b: active=1 donating=1 after=0

Fix it by excluding cgroups w/ active hweight < 2 from donating. Excluding
these extreme low hweight donations shouldn't affect work conservation in
any meaningful way.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: f1de2439ec ("blk-iocost: revamp donation amount determination")
Cc: stable@vger.kernel.org # v5.10+
Link: https://lore.kernel.org/r/Ybfh86iSvpWKxhVM@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-12-14 06:58:15 -07:00
arch parisc architecture build-, trace-, backtrace- and page table fixes 2021-11-14 11:53:59 -08:00
block iocost: Fix divide-by-zero on donation from low hweight cgroup 2021-12-14 06:58:15 -07:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Update to zstd-1.4.10 2021-11-13 15:32:30 -08:00
Documentation Devicetree fixes for v5.16, take 1: 2021-11-14 11:11:51 -08:00
drivers Revert "mtd_blkdevs: don't scan partitions for plain mtdblock" 2021-12-10 11:52:34 -07:00
fs Revert "mark pstore-blk as broken" 2021-11-16 17:23:42 -07:00
include Devicetree fixes for v5.16, take 1: 2021-11-14 11:11:51 -08:00
init kconfig: Add support for -Wimplicit-fallthrough 2021-11-14 13:27:30 -08:00
ipc ipc/ipc_sysctl.c: remove fallback for !CONFIG_PROC_SYSCTL 2021-11-09 10:02:53 -08:00
kernel A single fix for POSIX CPU timers to address a problem where POSIX CPU 2021-11-14 10:43:38 -08:00
lib Update to zstd-1.4.10 2021-11-13 15:32:30 -08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm Revert "mm: shmem: don't truncate page if memory failure happens" 2021-11-13 12:03:03 -08:00
net One notable change here is that async creates and unlinks introduced 2021-11-13 11:31:07 -08:00
samples Add gitignore file for samples/fanotify/ subdirectory 2021-11-07 11:19:24 -08:00
scripts coccinelle patches for 5.16-rc1 2021-11-13 10:45:17 -08:00
security net,lsm,selinux: revert the security_sctp_assoc_established() hook 2021-11-12 12:07:02 -05:00
sound sound fixes for 5.16-rc1 2021-11-12 12:17:30 -08:00
tools A single fix for static calls to make the trampoline patching more robust 2021-11-14 10:30:17 -08:00
usr initramfs: Check timestamp to prevent broken cpio archive 2021-10-24 13:48:40 +09:00
virt KVM: generalize "bugged" VM to "dead" VM 2021-11-11 10:35:26 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap Merge branch 'akpm' (patches from Andrew) 2021-11-09 10:11:53 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS - Add the model number of a new, Raptor Lake CPU, to intel-family.h 2021-11-14 09:29:03 -08:00
Makefile Linux 5.16-rc1 2021-11-14 13:56:52 -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.