caffd39d4f
commit ab6f762f0f53162d41497708b33c9a3236d3609e upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
84 lines
2.5 KiB
C
84 lines
2.5 KiB
C
/*
|
|
* internal.h - printk internal definitions
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public License
|
|
* as published by the Free Software Foundation; either version 2
|
|
* of the License, or (at your option) any later version.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
#include <linux/percpu.h>
|
|
|
|
#ifdef CONFIG_PRINTK
|
|
|
|
#define PRINTK_SAFE_CONTEXT_MASK 0x3fffffff
|
|
#define PRINTK_NMI_DIRECT_CONTEXT_MASK 0x40000000
|
|
#define PRINTK_NMI_CONTEXT_MASK 0x80000000
|
|
|
|
extern raw_spinlock_t logbuf_lock;
|
|
|
|
__printf(5, 0)
|
|
int vprintk_store(int facility, int level,
|
|
const char *dict, size_t dictlen,
|
|
const char *fmt, va_list args);
|
|
|
|
__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
|
|
__printf(1, 0) int vprintk_deferred(const char *fmt, va_list args);
|
|
__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
|
|
void __printk_safe_enter(void);
|
|
void __printk_safe_exit(void);
|
|
|
|
void printk_safe_init(void);
|
|
bool printk_percpu_data_ready(void);
|
|
|
|
#define printk_safe_enter_irqsave(flags) \
|
|
do { \
|
|
local_irq_save(flags); \
|
|
__printk_safe_enter(); \
|
|
} while (0)
|
|
|
|
#define printk_safe_exit_irqrestore(flags) \
|
|
do { \
|
|
__printk_safe_exit(); \
|
|
local_irq_restore(flags); \
|
|
} while (0)
|
|
|
|
#define printk_safe_enter_irq() \
|
|
do { \
|
|
local_irq_disable(); \
|
|
__printk_safe_enter(); \
|
|
} while (0)
|
|
|
|
#define printk_safe_exit_irq() \
|
|
do { \
|
|
__printk_safe_exit(); \
|
|
local_irq_enable(); \
|
|
} while (0)
|
|
|
|
void defer_console_output(void);
|
|
|
|
#else
|
|
|
|
__printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
|
|
|
|
/*
|
|
* In !PRINTK builds we still export logbuf_lock spin_lock, console_sem
|
|
* semaphore and some of console functions (console_unlock()/etc.), so
|
|
* printk-safe must preserve the existing local IRQ guarantees.
|
|
*/
|
|
#define printk_safe_enter_irqsave(flags) local_irq_save(flags)
|
|
#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
|
|
|
|
#define printk_safe_enter_irq() local_irq_disable()
|
|
#define printk_safe_exit_irq() local_irq_enable()
|
|
|
|
static inline void printk_safe_init(void) { }
|
|
static inline bool printk_percpu_data_ready(void) { return false; }
|
|
#endif /* CONFIG_PRINTK */
|