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printk changes for 5.18

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Merge tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Make %pK behave the same as %p for kptr_restrict == 0 also with
   no_hash_pointers parameter

 - Ignore the default console in the device tree also when console=null
   or console="" is used on the command line

 - Document console=null and console="" behavior

 - Prevent a deadlock and a livelock caused by console_lock in panic()

 - Make console_lock available for panicking CPU

 - Fast query for the next to-be-used sequence number

 - Use the expected return values in printk.devkmsg __setup handler

 - Use the correct atomic operations in wake_up_klogd() irq_work handler

 - Avoid possible unaligned access when handling %4cc printing format

* tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: fix return value of printk.devkmsg __setup handler
  vsprintf: Fix %pK with kptr_restrict == 0
  printk: make suppress_panic_printk static
  printk: Set console_set_on_cmdline=1 when __add_preferred_console() is called with user_specified == true
  Docs: printk: add 'console=null|""' to admin/kernel-parameters
  printk: use atomic updates for klogd work
  printk: Drop console_sem during panic
  printk: Avoid livelock with heavy printk during panic
  printk: disable optimistic spin during panic
  printk: Add panic_in_progress helper
  vsprintf: Move space out of string literals in fourcc_string()
  vsprintf: Fix potential unaligned access
  printk: ringbuffer: Improve prb_next_seq() performance
This commit is contained in:
Linus Torvalds 2022-03-23 10:54:27 -07:00
commit 3ef4ea3d84
5 changed files with 161 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Documentation/admin-guide/kernel-parameters.txt
View File

@ -724,6 +724,12 @@
hvc<n> Use the hypervisor console device <n>. This is for
both Xen and PowerPC hypervisors.
{ null | "" }
Use to disable console output, i.e., to have kernel
console messages discarded.
This must be the only console= parameter used on the
kernel command line.
If the device connected to the port is not a TTY but a braille
device, prepend "brl," before the device type, for instance
console=brl,ttyS0
@ -3516,8 +3522,7 @@
difficult since unequal pointers can no longer be
compared. However, if this command-line option is
specified, then all normal pointers will have their true
value printed. Pointers printed via %pK may still be
hashed. This option should only be specified when
value printed. This option should only be specified when
debugging the kernel. Please do not use on production
kernels.

85
kernel/printk/printk.c
View File

@ -93,6 +93,12 @@ EXPORT_SYMBOL_GPL(console_drivers);
*/
int __read_mostly suppress_printk;
/*
* During panic, heavy printk by other CPUs can delay the
* panic and risk deadlock on console resources.
*/
static int __read_mostly suppress_panic_printk;
#ifdef CONFIG_LOCKDEP
static struct lockdep_map console_lock_dep_map = {
.name = "console_lock"
@ -146,8 +152,10 @@ static int __control_devkmsg(char *str)
static int __init control_devkmsg(char *str)
{
if (__control_devkmsg(str) < 0)
if (__control_devkmsg(str) < 0) {
pr_warn("printk.devkmsg: bad option string '%s'\n", str);
return 1;
}
/*
* Set sysctl string accordingly:
@ -166,7 +174,7 @@ static int __init control_devkmsg(char *str)
*/
devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
return 0;
return 1;
}
__setup("printk.devkmsg=", control_devkmsg);
@ -257,6 +265,11 @@ static void __up_console_sem(unsigned long ip)
}
#define up_console_sem() __up_console_sem(_RET_IP_)
static bool panic_in_progress(void)
{
return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
}
/*
* This is used for debugging the mess that is the VT code by
* keeping track if we have the console semaphore held. It's
@ -1843,6 +1856,16 @@ static int console_trylock_spinning(void)
if (console_trylock())
return 1;
/*
* It's unsafe to spin once a panic has begun. If we are the
* panic CPU, we may have already halted the owner of the
* console_sem. If we are not the panic CPU, then we should
* avoid taking console_sem, so the panic CPU has a better
* chance of cleanly acquiring it later.
*/
if (panic_in_progress())
return 0;
printk_safe_enter_irqsave(flags);
raw_spin_lock(&console_owner_lock);
@ -2218,6 +2241,10 @@ asmlinkage int vprintk_emit(int facility, int level,
if (unlikely(suppress_printk))
return 0;
if (unlikely(suppress_panic_printk) &&
atomic_read(&panic_cpu) != raw_smp_processor_id())
return 0;
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
in_sched = true;
@ -2324,6 +2351,20 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
}
#endif
static void set_user_specified(struct console_cmdline *c, bool user_specified)
{
if (!user_specified)
return;
/*
* @c console was defined by the user on the command line.
* Do not clear when added twice also by SPCR or the device tree.
*/
c->user_specified = true;
/* At least one console defined by the user on the command line. */
console_set_on_cmdline = 1;
}
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options, bool user_specified)
{
@ -2340,8 +2381,7 @@ static int __add_preferred_console(char *name, int idx, char *options,
if (strcmp(c->name, name) == 0 && c->index == idx) {
if (!brl_options)
preferred_console = i;
if (user_specified)
c->user_specified = true;
set_user_specified(c, user_specified);
return 0;
}
}
@ -2351,7 +2391,7 @@ static int __add_preferred_console(char *name, int idx, char *options,
preferred_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
c->user_specified = user_specified;
set_user_specified(c, user_specified);
braille_set_options(c, brl_options);
c->index = idx;
@ -2417,7 +2457,6 @@ static int __init console_setup(char *str)
*s = 0;
__add_preferred_console(buf, idx, options, brl_options, true);
console_set_on_cmdline = 1;
return 1;
}
__setup("console=", console_setup);
@ -2573,6 +2612,25 @@ static int have_callable_console(void)
return 0;
}
/*
* 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();
}
/*
* Can we actually use the console at this time on this cpu?
*
@ -2603,6 +2661,7 @@ void console_unlock(void)
{
static char ext_text[CONSOLE_EXT_LOG_MAX];
static char text[CONSOLE_LOG_MAX];
static int panic_console_dropped;
unsigned long flags;
bool do_cond_resched, retry;
struct printk_info info;
@ -2657,6 +2716,10 @@ void console_unlock(void)
if (console_seq != r.info->seq) {
console_dropped += r.info->seq - console_seq;
console_seq = r.info->seq;
if (panic_in_progress() && panic_console_dropped++ > 10) {
suppress_panic_printk = 1;
pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
}
}
if (suppress_message_printing(r.info->level)) {
@ -2716,6 +2779,10 @@ void console_unlock(void)
if (handover)
return;
/* Allow panic_cpu to take over the consoles safely */
if (abandon_console_lock_in_panic())
break;
if (do_cond_resched)
cond_resched();
}
@ -2733,7 +2800,7 @@ void console_unlock(void)
* flush, no worries.
*/
retry = prb_read_valid(prb, next_seq, NULL);
if (retry && console_trylock())
if (retry && !abandon_console_lock_in_panic() && console_trylock())
goto again;
}
EXPORT_SYMBOL(console_unlock);
@ -3228,7 +3295,7 @@ static DEFINE_PER_CPU(int, printk_pending);
static void wake_up_klogd_work_func(struct irq_work *irq_work)
{
int pending = __this_cpu_xchg(printk_pending, 0);
int pending = this_cpu_xchg(printk_pending, 0);
if (pending & PRINTK_PENDING_OUTPUT) {
/* If trylock fails, someone else is doing the printing */
@ -3262,7 +3329,7 @@ void defer_console_output(void)
return;
preempt_disable();
__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}

52
kernel/printk/printk_ringbuffer.c
View File

@ -474,8 +474,10 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
* state has been re-checked. A memcpy() for all of @desc
* cannot be used because of the atomic_t @state_var field.
*/
memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos,
sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */
if (desc_out) {
memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos,
sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */
}
if (seq_out)
*seq_out = info->seq; /* also part of desc_read:C */
if (caller_id_out)
@ -528,7 +530,8 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */
d_state = get_desc_state(id, state_val);
out:
atomic_long_set(&desc_out->state_var, state_val);
if (desc_out)
atomic_long_set(&desc_out->state_var, state_val);
return d_state;
}
@ -1449,6 +1452,9 @@ static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id)
atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val,
DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */
/* Best effort to remember the last finalized @id. */
atomic_long_set(&desc_ring->last_finalized_id, id);
}
/**
@ -1657,7 +1663,12 @@ void prb_commit(struct prb_reserved_entry *e)
*/
void prb_final_commit(struct prb_reserved_entry *e)
{
struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
_prb_commit(e, desc_finalized);
/* Best effort to remember the last finalized @id. */
atomic_long_set(&desc_ring->last_finalized_id, e->id);
}
/*
@ -2005,9 +2016,39 @@ u64 prb_first_valid_seq(struct printk_ringbuffer *rb)
*/
u64 prb_next_seq(struct printk_ringbuffer *rb)
{
u64 seq = 0;
struct prb_desc_ring *desc_ring = &rb->desc_ring;
enum desc_state d_state;
unsigned long id;
u64 seq;
/* Search forward from the oldest descriptor. */
/* Check if the cached @id still points to a valid @seq. */
id = atomic_long_read(&desc_ring->last_finalized_id);
d_state = desc_read(desc_ring, id, NULL, &seq, NULL);
if (d_state == desc_finalized || d_state == desc_reusable) {
/*
* Begin searching after the last finalized record.
*
* On 0, the search must begin at 0 because of hack#2
* of the bootstrapping phase it is not known if a
* record at index 0 exists.
*/
if (seq != 0)
seq++;
} else {
/*
* The information about the last finalized sequence number
* has gone. It should happen only when there is a flood of
* new messages and the ringbuffer is rapidly recycled.
* Give up and start from the beginning.
*/
seq = 0;
}
/*
* The information about the last finalized @seq might be inaccurate.
* Search forward to find the current one.
*/
while (_prb_read_valid(rb, &seq, NULL, NULL))
seq++;
@ -2044,6 +2085,7 @@ void prb_init(struct printk_ringbuffer *rb,
rb->desc_ring.infos = infos;
atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits));
atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits));
atomic_long_set(&rb->desc_ring.last_finalized_id, DESC0_ID(descbits));
rb->text_data_ring.size_bits = textbits;
rb->text_data_ring.data = text_buf;

2
kernel/printk/printk_ringbuffer.h
View File

@ -75,6 +75,7 @@ struct prb_desc_ring {
struct printk_info *infos;
atomic_long_t head_id;
atomic_long_t tail_id;
atomic_long_t last_finalized_id;
};
/*
@ -258,6 +259,7 @@ static struct printk_ringbuffer name = { \
.infos = &_##name##_infos[0], \
.head_id = ATOMIC_INIT(DESC0_ID(descbits)), \
.tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \
.last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)), \
}, \
.text_data_ring = { \
.size_bits = (avgtextbits) + (descbits), \

49
lib/vsprintf.c
View File

@ -49,10 +49,15 @@
#include <asm/page.h> /* for PAGE_SIZE */
#include <asm/byteorder.h> /* cpu_to_le16 */
#include <asm/unaligned.h>
#include <linux/string_helpers.h>
#include "kstrtox.h"
/* Disable pointer hashing if requested */
bool no_hash_pointers __ro_after_init;
EXPORT_SYMBOL_GPL(no_hash_pointers);
static noinline unsigned long long simple_strntoull(const char *startp, size_t max_chars, char **endp, unsigned int base)
{
const char *cp;
@ -850,6 +855,19 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
return pointer_string(buf, end, (const void *)hashval, spec);
}
static char *default_pointer(char *buf, char *end, const void *ptr,
struct printf_spec spec)
{
/*
* default is to _not_ leak addresses, so hash before printing,
* unless no_hash_pointers is specified on the command line.
*/
if (unlikely(no_hash_pointers))
return pointer_string(buf, end, ptr, spec);
return ptr_to_id(buf, end, ptr, spec);
}
int kptr_restrict __read_mostly;
static noinline_for_stack
@ -859,7 +877,7 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
switch (kptr_restrict) {
case 0:
/* Handle as %p, hash and do _not_ leak addresses. */
return ptr_to_id(buf, end, ptr, spec);
return default_pointer(buf, end, ptr, spec);
case 1: {
const struct cred *cred;
@ -1763,7 +1781,7 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
char output[sizeof("0123 little-endian (0x01234567)")];
char *p = output;
unsigned int i;
u32 val;
u32 orig, val;
if (fmt[1] != 'c' || fmt[2] != 'c')
return error_string(buf, end, "(%p4?)", spec);
@ -1771,21 +1789,23 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
if (check_pointer(&buf, end, fourcc, spec))
return buf;
val = *fourcc & ~BIT(31);
orig = get_unaligned(fourcc);
val = orig & ~BIT(31);
for (i = 0; i < sizeof(*fourcc); i++) {
for (i = 0; i < sizeof(u32); i++) {
unsigned char c = val >> (i * 8);
/* Print non-control ASCII characters as-is, dot otherwise */
*p++ = isascii(c) && isprint(c) ? c : '.';
}
strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
*p++ = ' ';
strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
p += strlen(p);
*p++ = ' ';
*p++ = '(';
p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, sizeof(u32));
p = special_hex_number(p, output + sizeof(output) - 2, orig, sizeof(u32));
*p++ = ')';
*p = '\0';
@ -2225,10 +2245,6 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
return widen_string(buf, buf - buf_start, end, spec);
}
/* Disable pointer hashing if requested */
bool no_hash_pointers __ro_after_init;
EXPORT_SYMBOL_GPL(no_hash_pointers);
int __init no_hash_pointers_enable(char *str)
{
if (no_hash_pointers)
@ -2457,7 +2473,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
case 'e':
/* %pe with a non-ERR_PTR gets treated as plain %p */
if (!IS_ERR(ptr))
break;
return default_pointer(buf, end, ptr, spec);
return err_ptr(buf, end, ptr, spec);
case 'u':
case 'k':
@ -2467,16 +2483,9 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
default:
return error_string(buf, end, "(einval)", spec);
}
default:
return default_pointer(buf, end, ptr, spec);
}
/*
* default is to _not_ leak addresses, so hash before printing,
* unless no_hash_pointers is specified on the command line.
*/
if (unlikely(no_hash_pointers))
return pointer_string(buf, end, ptr, spec);
else
return ptr_to_id(buf, end, ptr, spec);
}
/*