XOR/mint0x33
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions
A Exynos 9610 Kernel ported from the Exynos 9611
733983 commits 1 branch 0 tags 1.6 GiB
Find a file
Thomas Gleixner d21f4dae47 alarmtimer: Prevent starvation by small intervals and SIG_IGN 
commit d125d1349abeb46945dc5e98f7824bf688266f13 upstream.

syzbot reported a RCU stall which is caused by setting up an alarmtimer
with a very small interval and ignoring the signal. The reproducer arms the
alarm timer with a relative expiry of 8ns and an interval of 9ns. Not a
problem per se, but that's an issue when the signal is ignored because then
the timer is immediately rearmed because there is no way to delay that
rearming to the signal delivery path.  See posix_timer_fn() and commit
58229a1899 ("posix-timers: Prevent softirq starvation by small intervals
and SIG_IGN") for details.

The reproducer does not set SIG_IGN explicitely, but it sets up the timers
signal with SIGCONT. That has the same effect as explicitely setting
SIG_IGN for a signal as SIGCONT is ignored if there is no handler set and
the task is not ptraced.

The log clearly shows that:

   [pid  5102] --- SIGCONT {si_signo=SIGCONT, si_code=SI_TIMER, si_timerid=0, si_overrun=316014, si_int=0, si_ptr=NULL} ---

It works because the tasks are traced and therefore the signal is queued so
the tracer can see it, which delays the restart of the timer to the signal
delivery path. But then the tracer is killed:

   [pid  5087] kill(-5102, SIGKILL <unfinished ...>
   ...
   ./strace-static-x86_64: Process 5107 detached

and after it's gone the stall can be observed:

   syzkaller login: [   79.439102][    C0] hrtimer: interrupt took 68471 ns
   [  184.460538][    C1] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
   ...
   [  184.658237][    C1] rcu: Stack dump where RCU GP kthread last ran:
   [  184.664574][    C1] Sending NMI from CPU 1 to CPUs 0:
   [  184.669821][    C0] NMI backtrace for cpu 0
   [  184.669831][    C0] CPU: 0 PID: 5108 Comm: syz-executor192 Not tainted 6.2.0-rc6-next-20230203-syzkaller #0
   ...
   [  184.670036][    C0] Call Trace:
   [  184.670041][    C0]  <IRQ>
   [  184.670045][    C0]  alarmtimer_fired+0x327/0x670

posix_timer_fn() prevents that by checking whether the interval for
timers which have the signal ignored is smaller than a jiffie and
artifically delay it by shifting the next expiry out by a jiffie. That's
accurate vs. the overrun accounting, but slightly inaccurate
vs. timer_gettimer(2).

The comment in that function says what needs to be done and there was a fix
available for the regular userspace induced SIG_IGN mechanism, but that did
not work due to the implicit ignore for SIGCONT and similar signals. This
needs to be worked on, but for now the only available workaround is to do
exactly what posix_timer_fn() does:

Increase the interval of self-rearming timers, which have their signal
ignored, to at least a jiffie.

Interestingly this has been fixed before via commit ff86bf0c65
("alarmtimer: Rate limit periodic intervals") already, but that fix got
lost in a later rework.

Reported-by: syzbot+b9564ba6e8e00694511b@syzkaller.appspotmail.com
Fixes: f2c45807d3 ("alarmtimer: Switch over to generic set/get/rearm routine")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87k00q1no2.ffs@tglx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-02-25 11:50:31 +01:00
arch powerpc: dts: t208x: Disable 10G on MAC1 and MAC2 2023-02-25 11:50:31 +01:00
block blk-mq: fix possible memleak when register 'hctx' failed 2023-01-18 09:26:32 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:46:44 +02:00
crypto crypto: drbg - make reseeding from get_random_bytes() synchronous 2022-06-25 11:46:41 +02:00
Documentation docs: Fix path paste-o for /sys/kernel/warn_count 2023-02-06 07:46:35 +01:00
drivers wifi: rtl8xxxu: gen2: Turn on the rate control 2023-02-25 11:50:30 +01:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs nilfs2: fix underflow in second superblock position calculations 2023-02-22 12:46:07 +01:00
include random: always mix cycle counter in add_latent_entropy() 2023-02-25 11:50:31 +01:00
init random: handle latent entropy and command line from random_init() 2022-06-25 11:46:40 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:16:33 +01:00
kernel alarmtimer: Prevent starvation by small intervals and SIG_IGN 2023-02-25 11:50:31 +01:00
lib test_firmware: fix memory leak in test_firmware_init() 2023-01-18 09:26:24 +01:00
mm migrate: hugetlb: check for hugetlb shared PMD in node migration 2023-02-22 12:46:04 +01:00
net ipv6: Fix tcp socket connection with DSCP. 2023-02-22 12:46:06 +01:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:40:31 +01:00
scripts kconfig: display recursive dependency resolution hint just once 2022-12-08 11:16:30 +01:00
security tomoyo: fix broken dependency on *.conf.default 2023-02-06 07:46:28 +01:00
sound ALSA: hda/conexant: add a new hda codec SN6180 2023-02-22 12:46:05 +01:00
tools tools/virtio: fix the vringh test for virtio ring changes 2023-02-22 12:46:05 +01:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-11-03 23:50:50 +09:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild
Kconfig
MAINTAINERS MAINTAINERS: co-maintain random.c 2022-06-25 11:46:29 +02:00
Makefile Linux 4.14.306 2023-02-22 12:46:07 +01:00
README

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.