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author | Sergey Senozhatsky <sergey.senozhatsky@gmail.com> | 2020-03-03 12:30:02 +0100 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-10 22:18:57 +0200 |
commit | ab6f762f0f53162d41497708b33c9a3236d3609e (patch) | |
tree | e0d405ac3f1a4c99cc46609cb24bc64ee5cfea19 /lib/test_kasan.c | |
parent | Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebi... (diff) | |
download | linux-ab6f762f0f53162d41497708b33c9a3236d3609e.tar.xz linux-ab6f762f0f53162d41497708b33c9a3236d3609e.zip |
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 1b710b1b10ef ("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>
Diffstat (limited to '')
0 files changed, 0 insertions, 0 deletions