printk changes for 6.6

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Merge tag 'printk-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Do not try to get the console lock when it is not need or useful in
   panic()

 - Replace the global console_suspended state by a per-console flag

 - Export symbols needed for dumping the raw printk buffer in panic()

 - Fix documentation of printf formats for integer types

 - Moved Sergey Senozhatsky to the reviewer role

 - Misc cleanups

* tag 'printk-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: export symbols for debug modules
  lib: test_scanf: Add explicit type cast to result initialization in test_number_prefix()
  printk: ringbuffer: Fix truncating buffer size min_t cast
  printk: Rename abandon_console_lock_in_panic() to other_cpu_in_panic()
  printk: Add per-console suspended state
  printk: Consolidate console deferred printing
  printk: Do not take console lock for console_flush_on_panic()
  printk: Keep non-panic-CPUs out of console lock
  printk: Reduce console_unblank() usage in unsafe scenarios
  kdb: Do not assume write() callback available
  docs: printk-formats: Treat char as always unsigned
  docs: printk-formats: Fix hex printing of signed values
  MAINTAINERS: adjust printk/vsprintf entries
This commit is contained in:
Linus Torvalds 2023-09-04 13:20:19 -07:00
commit 3c31041e37
9 changed files with 167 additions and 81 deletions

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@ -15,9 +15,10 @@ Integer types
If variable is of Type, use printk format specifier:
------------------------------------------------------------
char %d or %x
signed char %d or %hhx
unsigned char %u or %x
short int %d or %x
char %u or %x
short int %d or %hx
unsigned short int %u or %x
int %d or %x
unsigned int %u or %x
@ -27,9 +28,9 @@ Integer types
unsigned long long %llu or %llx
size_t %zu or %zx
ssize_t %zd or %zx
s8 %d or %x
s8 %d or %hhx
u8 %u or %x
s16 %d or %x
s16 %d or %hx
u16 %u or %x
s32 %d or %x
u32 %u or %x

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@ -17176,9 +17176,9 @@ F: kernel/sched/psi.c
PRINTK
M: Petr Mladek <pmladek@suse.com>
M: Sergey Senozhatsky <senozhatsky@chromium.org>
R: Steven Rostedt <rostedt@goodmis.org>
R: John Ogness <john.ogness@linutronix.de>
R: Sergey Senozhatsky <senozhatsky@chromium.org>
S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux.git
F: include/linux/printk.h
@ -23072,9 +23072,9 @@ F: drivers/net/vrf.c
VSPRINTF
M: Petr Mladek <pmladek@suse.com>
M: Steven Rostedt <rostedt@goodmis.org>
M: Sergey Senozhatsky <senozhatsky@chromium.org>
R: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
R: Rasmus Villemoes <linux@rasmusvillemoes.dk>
R: Sergey Senozhatsky <senozhatsky@chromium.org>
S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux.git
F: Documentation/core-api/printk-formats.rst

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@ -154,6 +154,8 @@ static inline int con_debug_leave(void)
* receiving the printk spam for obvious reasons.
* @CON_EXTENDED: The console supports the extended output format of
* /dev/kmesg which requires a larger output buffer.
* @CON_SUSPENDED: Indicates if a console is suspended. If true, the
* printing callbacks must not be called.
*/
enum cons_flags {
CON_PRINTBUFFER = BIT(0),
@ -163,6 +165,7 @@ enum cons_flags {
CON_ANYTIME = BIT(4),
CON_BRL = BIT(5),
CON_EXTENDED = BIT(6),
CON_SUSPENDED = BIT(7),
};
/**

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@ -590,6 +590,8 @@ static void kdb_msg_write(const char *msg, int msg_len)
continue;
if (c == dbg_io_ops->cons)
continue;
if (!c->write)
continue;
/*
* Set oops_in_progress to encourage the console drivers to
* disregard their internal spin locks: in the current calling

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@ -103,3 +103,5 @@ struct printk_message {
u64 seq;
unsigned long dropped;
};
bool other_cpu_in_panic(void);

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@ -88,7 +88,7 @@ EXPORT_SYMBOL(oops_in_progress);
static DEFINE_MUTEX(console_mutex);
/*
* console_sem protects updates to console->seq and console_suspended,
* console_sem protects updates to console->seq
* and also provides serialization for console printing.
*/
static DEFINE_SEMAPHORE(console_sem, 1);
@ -361,7 +361,7 @@ static bool panic_in_progress(void)
* paths in the console code where we end up in places I want
* locked without the console semaphore held).
*/
static int console_locked, console_suspended;
static int console_locked;
/*
* Array of consoles built from command line options (console=)
@ -538,12 +538,14 @@ char *log_buf_addr_get(void)
{
return log_buf;
}
EXPORT_SYMBOL_GPL(log_buf_addr_get);
/* Return log buffer size */
u32 log_buf_len_get(void)
{
return log_buf_len;
}
EXPORT_SYMBOL_GPL(log_buf_len_get);
/*
* Define how much of the log buffer we could take at maximum. The value
@ -2308,7 +2310,11 @@ asmlinkage int vprintk_emit(int facility, int level,
preempt_enable();
}
wake_up_klogd();
if (in_sched)
defer_console_output();
else
wake_up_klogd();
return printed_len;
}
EXPORT_SYMBOL(vprintk_emit);
@ -2547,22 +2553,46 @@ MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to hig
*/
void suspend_console(void)
{
struct console *con;
if (!console_suspend_enabled)
return;
pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
pr_flush(1000, true);
console_lock();
console_suspended = 1;
up_console_sem();
console_list_lock();
for_each_console(con)
console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
console_list_unlock();
/*
* Ensure that all SRCU list walks have completed. All printing
* contexts must be able to see that they are suspended so that it
* is guaranteed that all printing has stopped when this function
* completes.
*/
synchronize_srcu(&console_srcu);
}
void resume_console(void)
{
struct console *con;
if (!console_suspend_enabled)
return;
down_console_sem();
console_suspended = 0;
console_unlock();
console_list_lock();
for_each_console(con)
console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
console_list_unlock();
/*
* Ensure that all SRCU list walks have completed. All printing
* contexts must be able to see they are no longer suspended so
* that they are guaranteed to wake up and resume printing.
*/
synchronize_srcu(&console_srcu);
pr_flush(1000, true);
}
@ -2585,6 +2615,26 @@ static int console_cpu_notify(unsigned int cpu)
return 0;
}
/*
* Return true if a panic is in progress on a remote CPU.
*
* On true, the local CPU should immediately release any printing resources
* that may be needed by the panic CPU.
*/
bool other_cpu_in_panic(void)
{
if (!panic_in_progress())
return false;
/*
* We can use raw_smp_processor_id() here because it is impossible for
* the task to be migrated to the panic_cpu, or away from it. If
* panic_cpu has already been set, and we're not currently executing on
* that CPU, then we never will be.
*/
return atomic_read(&panic_cpu) != raw_smp_processor_id();
}
/**
* console_lock - block the console subsystem from printing
*
@ -2597,9 +2647,11 @@ void console_lock(void)
{
might_sleep();
/* On panic, the console_lock must be left to the panic cpu. */
while (other_cpu_in_panic())
msleep(1000);
down_console_sem();
if (console_suspended)
return;
console_locked = 1;
console_may_schedule = 1;
}
@ -2615,12 +2667,11 @@ EXPORT_SYMBOL(console_lock);
*/
int console_trylock(void)
{
/* On panic, the console_lock must be left to the panic cpu. */
if (other_cpu_in_panic())
return 0;
if (down_trylock_console_sem())
return 0;
if (console_suspended) {
up_console_sem();
return 0;
}
console_locked = 1;
console_may_schedule = 0;
return 1;
@ -2633,25 +2684,6 @@ int is_console_locked(void)
}
EXPORT_SYMBOL(is_console_locked);
/*
* Return true when this CPU should unlock console_sem without pushing all
* messages to the console. This reduces the chance that the console is
* locked when the panic CPU tries to use it.
*/
static bool abandon_console_lock_in_panic(void)
{
if (!panic_in_progress())
return false;
/*
* We can use raw_smp_processor_id() here because it is impossible for
* the task to be migrated to the panic_cpu, or away from it. If
* panic_cpu has already been set, and we're not currently executing on
* that CPU, then we never will be.
*/
return atomic_read(&panic_cpu) != raw_smp_processor_id();
}
/*
* Check if the given console is currently capable and allowed to print
* records.
@ -2665,6 +2697,9 @@ static inline bool console_is_usable(struct console *con)
if (!(flags & CON_ENABLED))
return false;
if ((flags & CON_SUSPENDED))
return false;
if (!con->write)
return false;
@ -2948,7 +2983,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
any_progress = true;
/* Allow panic_cpu to take over the consoles safely. */
if (abandon_console_lock_in_panic())
if (other_cpu_in_panic())
goto abandon;
if (do_cond_resched)
@ -2983,11 +3018,6 @@ void console_unlock(void)
bool flushed;
u64 next_seq;
if (console_suspended) {
up_console_sem();
return;
}
/*
* Console drivers are called with interrupts disabled, so
* @console_may_schedule should be cleared before; however, we may
@ -3045,9 +3075,27 @@ EXPORT_SYMBOL(console_conditional_schedule);
void console_unblank(void)
{
bool found_unblank = false;
struct console *c;
int cookie;
/*
* First check if there are any consoles implementing the unblank()
* callback. If not, there is no reason to continue and take the
* console lock, which in particular can be dangerous if
* @oops_in_progress is set.
*/
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {
found_unblank = true;
break;
}
}
console_srcu_read_unlock(cookie);
if (!found_unblank)
return;
/*
* Stop console printing because the unblank() callback may
* assume the console is not within its write() callback.
@ -3056,6 +3104,16 @@ void console_unblank(void)
* In that case, attempt a trylock as best-effort.
*/
if (oops_in_progress) {
/* Semaphores are not NMI-safe. */
if (in_nmi())
return;
/*
* Attempting to trylock the console lock can deadlock
* if another CPU was stopped while modifying the
* semaphore. "Hope and pray" that this is not the
* current situation.
*/
if (down_trylock_console_sem() != 0)
return;
} else
@ -3085,14 +3143,24 @@ void console_unblank(void)
*/
void console_flush_on_panic(enum con_flush_mode mode)
{
bool handover;
u64 next_seq;
/*
* If someone else is holding the console lock, trylock will fail
* and may_schedule may be set. Ignore and proceed to unlock so
* that messages are flushed out. As this can be called from any
* context and we don't want to get preempted while flushing,
* ensure may_schedule is cleared.
* Ignore the console lock and flush out the messages. Attempting a
* trylock would not be useful because:
*
* - if it is contended, it must be ignored anyway
* - console_lock() and console_trylock() block and fail
* respectively in panic for non-panic CPUs
* - semaphores are not NMI-safe
*/
/*
* If another context is holding the console lock,
* @console_may_schedule might be set. Clear it so that
* this context does not call cond_resched() while flushing.
*/
console_trylock();
console_may_schedule = 0;
if (mode == CONSOLE_REPLAY_ALL) {
@ -3105,15 +3173,15 @@ void console_flush_on_panic(enum con_flush_mode mode)
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
/*
* If the above console_trylock() failed, this is an
* unsynchronized assignment. But in that case, the
* This is an unsynchronized assignment, but the
* kernel is in "hope and pray" mode anyway.
*/
c->seq = seq;
}
console_srcu_read_unlock(cookie);
}
console_unlock();
console_flush_all(false, &next_seq, &handover);
}
/*
@ -3679,8 +3747,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
/*
* Hold the console_lock to guarantee safe access to
* console->seq and to prevent changes to @console_suspended
* until all consoles have been processed.
* console->seq.
*/
console_lock();
@ -3688,6 +3755,11 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
for_each_console_srcu(c) {
if (con && con != c)
continue;
/*
* If consoles are not usable, it cannot be expected
* that they make forward progress, so only increment
* @diff for usable consoles.
*/
if (!console_is_usable(c))
continue;
printk_seq = c->seq;
@ -3696,18 +3768,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
}
console_srcu_read_unlock(cookie);
/*
* If consoles are suspended, it cannot be expected that they
* make forward progress, so timeout immediately. @diff is
* still used to return a valid flush status.
*/
if (console_suspended)
remaining = 0;
else if (diff != last_diff && reset_on_progress)
if (diff != last_diff && reset_on_progress)
remaining = timeout_ms;
console_unlock();
/* Note: @diff is 0 if there are no usable consoles. */
if (diff == 0 || remaining == 0)
break;
@ -3741,7 +3807,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
* printer has been seen to make some forward progress.
*
* Context: Process context. May sleep while acquiring console lock.
* Return: true if all enabled printers are caught up.
* Return: true if all usable printers are caught up.
*/
static bool pr_flush(int timeout_ms, bool reset_on_progress)
{
@ -3798,11 +3864,33 @@ static void __wake_up_klogd(int val)
preempt_enable();
}
/**
* wake_up_klogd - Wake kernel logging daemon
*
* Use this function when new records have been added to the ringbuffer
* and the console printing of those records has already occurred or is
* known to be handled by some other context. This function will only
* wake the logging daemon.
*
* Context: Any context.
*/
void wake_up_klogd(void)
{
__wake_up_klogd(PRINTK_PENDING_WAKEUP);
}
/**
* defer_console_output - Wake kernel logging daemon and trigger
* console printing in a deferred context
*
* Use this function when new records have been added to the ringbuffer,
* this context is responsible for console printing those records, but
* the current context is not allowed to perform the console printing.
* Trigger an irq_work context to perform the console printing. This
* function also wakes the logging daemon.
*
* Context: Any context.
*/
void defer_console_output(void)
{
/*
@ -3819,12 +3907,7 @@ void printk_trigger_flush(void)
int vprintk_deferred(const char *fmt, va_list args)
{
int r;
r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
defer_console_output();
return r;
return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
}
int _printk_deferred(const char *fmt, ...)

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@ -1735,7 +1735,7 @@ static bool copy_data(struct prb_data_ring *data_ring,
if (!buf || !buf_size)
return true;
data_size = min_t(u16, buf_size, len);
data_size = min_t(unsigned int, buf_size, len);
memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */
return true;

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@ -38,13 +38,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
* Use the main logbuf even in NMI. But avoid calling console
* drivers that might have their own locks.
*/
if (this_cpu_read(printk_context) || in_nmi()) {
int len;
len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
defer_console_output();
return len;
}
if (this_cpu_read(printk_context) || in_nmi())
return vprintk_deferred(fmt, args);
/* No obstacles. */
return vprintk_default(fmt, args);

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@ -606,7 +606,7 @@ static void __init numbers_slice(void)
#define test_number_prefix(T, str, scan_fmt, expect0, expect1, n_args, fn) \
do { \
const T expect[2] = { expect0, expect1 }; \
T result[2] = {~expect[0], ~expect[1]}; \
T result[2] = { (T)~expect[0], (T)~expect[1] }; \
\
_test(fn, &expect, str, scan_fmt, n_args, &result[0], &result[1]); \
} while (0)