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
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braille.c	printk: Replace strncmp() with str_has_prefix()	2019-08-16 09:54:08 +02:00
braille.h	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
console_cmdline.h	printk: Fix preferred console selection with multiple matches	2020-02-18 09:34:42 +01:00
internal.h	printk: rename vprintk_func to vprintk	2021-03-30 15:21:18 +02:00
Makefile	printk: add lockless ringbuffer	2020-07-10 08:48:19 +02:00
printk_ringbuffer.c	Merge branch 'printk-rework' into for-linus	2021-01-21 16:06:21 +01:00
printk_ringbuffer.h	printk: rectify kernel-doc for prb_rec_init_wr()	2021-01-26 11:17:51 +01:00
printk_safe.c	printk: Move EXPORT_SYMBOL() closer to vprintk definition	2021-06-16 10:42:19 +02:00
printk.c	printk/console: Check consistent sequence number when handling race in console_unlock()	2021-07-08 18:45:35 +02:00