Sergey Senozhatsky ab6f762f0f printk: queue wake_up_klogd irq_work only if per-CPU areas are ready ... printk_deferred(), similarly to printk_safe/printk_nmi, does not immediately attempt to print a new message on the consoles, avoiding calls into non-reentrant kernel paths, e.g. scheduler or timekeeping, which potentially can deadlock the system. Those printk() flavors, instead, rely on per-CPU flush irq_work to print messages from safer contexts. For same reasons (recursive scheduler or timekeeping calls) printk() uses per-CPU irq_work in order to wake up user space syslog/kmsg readers. However, only printk_safe/printk_nmi do make sure that per-CPU areas have been initialised and that it's safe to modify per-CPU irq_work. This means that, for instance, should printk_deferred() be invoked "too early", that is before per-CPU areas are initialised, printk_deferred() will perform illegal per-CPU access. Lech Perczak [0] reports that after commit 1b710b1b10 ("char/random: silence a lockdep splat with printk()") user-space syslog/kmsg readers are not able to read new kernel messages. The reason is printk_deferred() being called too early (as was pointed out by Petr and John). Fix printk_deferred() and do not queue per-CPU irq_work before per-CPU areas are initialized. Link: https://lore.kernel.org/lkml/aa0732c6-5c4e-8a8b-a1c1-75ebe3dca05b@camlintechnologies.com/ Reported-by: Lech Perczak <l.perczak@camlintechnologies.com> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Tested-by: Jann Horn <jannh@google.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Ogness <john.ogness@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2020-04-10 13:18:57 -07:00
..
calibrate.c
do_mounts_initrd.c	init: unify opening /dev/console as stdin/stdout/stderr	2019-12-12 18:58:24 +01:00
do_mounts_md.c
do_mounts_rd.c
do_mounts.c	block: remove __bdevname	2020-03-24 07:57:07 -06:00
do_mounts.h
init_task.c	exec: Add exec_update_mutex to replace cred_guard_mutex	2020-03-25 10:03:36 -05:00
initramfs.c	arm64: use generic free_initrd_mem()	2019-10-16 13:55:25 +01:00
Kconfig	arm64 fixes:	2020-04-09 11:04:16 -07:00
main.c	printk: queue wake_up_klogd irq_work only if per-CPU areas are ready	2020-04-10 13:18:57 -07:00
Makefile
noinitramfs.c
version.c