mainlining shenanigans
Go to file
Petr Mladek 11e4b63abb printk/console: Check consistent sequence number when handling race in console_unlock()
The standard printk() tries to flush the message to the console
immediately. It tries to take the console lock. If the lock is
already taken then the current owner is responsible for flushing
even the new message.

There is a small race window between checking whether a new message is
available and releasing the console lock. It is solved by re-checking
the state after releasing the console lock. If the check is positive
then console_unlock() tries to take the lock again and process the new
message as well.

The commit 996e966640 ("printk: remove logbuf_lock") causes that
console_seq is not longer read atomically. As a result, the re-check might
be done with an inconsistent 64-bit index.

Solve it by using the last sequence number that has been checked under
the console lock. In the worst case, it will take the lock again only
to realized that the new message has already been proceed. But it
was possible even before.

The variable next_seq is marked as __maybe_unused to call down compiler
warning when CONFIG_PRINTK is not defined.

Fixes: commit 996e966640 ("printk: remove logbuf_lock")
Reported-by: kernel test robot <lkp@intel.com>  # unused next_seq warning
Cc: stable@vger.kernel.org # 5.13
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20210702150657.26760-1-pmladek@suse.com
2021-07-08 18:45:35 +02:00
arch hyperv-next for 5.14 2021-06-29 11:21:35 -07:00
block sched: Change task_struct::state 2021-06-18 11:43:09 +02:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-06-28 16:04:56 -07:00
Documentation printk changes for 5.14 2021-06-29 12:07:18 -07:00
drivers printk changes for 5.14 2021-06-29 12:07:18 -07:00
fs printk changes for 5.14 2021-06-29 12:07:18 -07:00
include printk changes for 5.14 2021-06-29 12:07:18 -07:00
init sched: Change task_struct::state 2021-06-18 11:43:09 +02:00
ipc Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-06-28 20:39:26 -07:00
kernel printk/console: Check consistent sequence number when handling race in console_unlock() 2021-07-08 18:45:35 +02:00
lib printk changes for 5.14 2021-06-29 12:07:18 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-06-28 20:39:26 -07:00
net hyperv-next for 5.14 2021-06-29 11:21:35 -07:00
samples This was a reasonably active cycle for documentation; this pull includes: 2021-06-28 16:53:05 -07:00
scripts This was a reasonably active cycle for documentation; this pull includes: 2021-06-28 16:53:05 -07:00
security integrity-v5.14 2021-06-28 16:15:50 -07:00
sound spi: Updates for v5.14 2021-06-28 11:10:20 -07:00
tools printk changes for 5.14 2021-06-29 12:07:18 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt ARM: 2021-06-28 15:40:51 -07:00
.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 m68k updates for v5.14 2021-06-28 14:01:03 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
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 printk changes for 5.14 2021-06-29 12:07:18 -07:00
Makefile arm64 updates for 5.14 2021-06-28 14:04:24 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.