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Petr Mladek 2a7ad49ad2 tracing: Initialize iter->seq after zeroing in tracing_read_pipe() [ Upstream commit `d303de1fcf` ] A customer reported the following softlockup: [899688.160002] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [test.sh:16464] [899688.160002] CPU: 0 PID: 16464 Comm: test.sh Not tainted 4.12.14-6.23-azure #1 SLE12-SP4 [899688.160002] RIP: 0010:up_write+0x1a/0x30 [899688.160002] Kernel panic - not syncing: softlockup: hung tasks [899688.160002] RIP: 0010:up_write+0x1a/0x30 [899688.160002] RSP: 0018:ffffa86784d4fde8 EFLAGS: 00000257 ORIG_RAX: ffffffffffffff12 [899688.160002] RAX: ffffffff970fea00 RBX: 0000000000000001 RCX: 0000000000000000 [899688.160002] RDX: ffffffff00000001 RSI: 0000000000000080 RDI: ffffffff970fea00 [899688.160002] RBP: ffffffffffffffff R08: ffffffffffffffff R09: 0000000000000000 [899688.160002] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8b59014720d8 [899688.160002] R13: ffff8b59014720c0 R14: ffff8b5901471090 R15: ffff8b5901470000 [899688.160002] tracing_read_pipe+0x336/0x3c0 [899688.160002] __vfs_read+0x26/0x140 [899688.160002] vfs_read+0x87/0x130 [899688.160002] SyS_read+0x42/0x90 [899688.160002] do_syscall_64+0x74/0x160 It caught the process in the middle of trace_access_unlock(). There is no loop. So, it must be looping in the caller tracing_read_pipe() via the "waitagain" label. Crashdump analyze uncovered that iter->seq was completely zeroed at this point, including iter->seq.seq.size. It means that print_trace_line() was never able to print anything and there was no forward progress. The culprit seems to be in the code: /* reset all but tr, trace, and overruns */ memset(&iter->seq, 0, sizeof(struct trace_iterator) - offsetof(struct trace_iterator, seq)); It was added by the commit `53d0aa7730` ("ftrace: add logic to record overruns"). It was v2.6.27-rc1. It was the time when iter->seq looked like: struct trace_seq { unsigned char buffer[PAGE_SIZE]; unsigned int len; }; There was no "size" variable and zeroing was perfectly fine. The solution is to reinitialize the structure after or without zeroing. Link: http://lkml.kernel.org/r/20191011142134.11997-1-pmladek@suse.com Signed-off-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2019-11-06 12:43:20 +01:00
arch	s390/uaccess: avoid (false positive) compiler warnings	2019-11-06 12:43:19 +01:00
block	blk-mq: move cancel of requeue_work to the front of blk_exit_queue	2019-10-05 12:47:37 +02:00
certs	Replace magic for trusting the secondary keyring with #define	2018-09-09 19:55:54 +02:00
crypto	crypto: skcipher - Unmap pages after an external error	2019-10-11 18:18:32 +02:00
Documentation	x86/xen: Return from panic notifier	2019-11-06 12:43:13 +01:00
drivers	nbd: fix possible sysfs duplicate warning	2019-11-06 12:43:18 +01:00
firmware	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
fs	NFSv4: Fix leak of clp->cl_acceptor string	2019-11-06 12:43:18 +01:00
include	scsi: core: save/restore command resid for error handling	2019-10-29 09:17:31 +01:00
init	init: initialize jump labels before command line option parsing	2019-05-16 19:42:23 +02:00
ipc	ipc/mqueue.c: only perform resource calculation if user valid	2019-08-06 19:05:24 +02:00
kernel	tracing: Initialize iter->seq after zeroing in tracing_read_pipe()	2019-11-06 12:43:20 +01:00
lib	kmemleak: increase DEBUG_KMEMLEAK_EARLY_LOG_SIZE default to 16K	2019-10-07 18:55:15 +02:00
mm	hugetlbfs: don't access uninitialized memmaps in pfn_range_valid_gigantic()	2019-10-29 09:17:39 +01:00
net	mac80211: Reject malformed SSID elements	2019-10-29 09:17:35 +01:00
samples	samples, bpf: fix to change the buffer size for read()	2019-07-21 09:04:17 +02:00
scripts	scripts/setlocalversion: Improve -dirty check with git-status --no-optional-locks	2019-11-06 12:42:55 +01:00
security	ima: always return negative code for error	2019-10-11 18:18:37 +02:00
sound	ALSA: hda/realtek - Apply ALC294 hp init also for S4 resume	2019-11-06 12:42:57 +01:00
tools	perf jevents: Fix period for Intel fixed counters	2019-11-06 12:43:04 +01:00
usr	kbuild: clean compressed initramfs image	2019-10-07 18:55:14 +02:00
virt	KVM: coalesced_mmio: add bounds checking	2019-09-21 07:15:28 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes	.gitattributes: set git diff driver for C source code files	2016-10-07 18:46:30 -07:00
.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	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
Kconfig	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
MAINTAINERS	USB: rio500: Remove Rio 500 kernel driver	2019-10-17 13:43:20 -07:00
Makefile	Linux 4.14.151	2019-10-29 09:17:49 +01:00
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.