diff options
| author | Sergey Senozhatsky <sergey.senozhatsky@gmail.com> | 2020-03-03 20:30:02 +0900 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-10 13:18:57 -0700 |
| commit | ab6f762f0f53162d41497708b33c9a3236d3609e (patch) | |
| tree | e0d405ac3f1a4c99cc46609cb24bc64ee5cfea19 /include | |
| parent | 87ad46e601340394cd75c1c79b19ca906f82c543 (diff) | |
| download | linux-ab6f762f0f53162d41497708b33c9a3236d3609e.tar.bz2 | |
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 'include')
| -rw-r--r-- | include/linux/printk.h | 5 |
1 files changed, 0 insertions, 5 deletions
diff --git a/include/linux/printk.h b/include/linux/printk.h index 1e6108b8d15f..e061635e0409 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -202,7 +202,6 @@ __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...); void dump_stack_print_info(const char *log_lvl); void show_regs_print_info(const char *log_lvl); extern asmlinkage void dump_stack(void) __cold; -extern void printk_safe_init(void); extern void printk_safe_flush(void); extern void printk_safe_flush_on_panic(void); #else @@ -269,10 +268,6 @@ static inline void dump_stack(void) { } -static inline void printk_safe_init(void) -{ -} - static inline void printk_safe_flush(void) { } |