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printk: add syslog_lock

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The global variables @syslog_seq, @syslog_partial, @syslog_time
and write access to @clear_seq are protected by @logbuf_lock.
Once @logbuf_lock is removed, these variables will need their
own synchronization method. Introduce @syslog_lock for this
purpose.

@syslog_lock is a raw_spin_lock for now. This simplifies the
transition to removing @logbuf_lock. Once @logbuf_lock and the
safe buffers are removed, @syslog_lock can change to spin_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210303101528.29901-11-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2021-03-03 11:15:23 +01:00 committed by Petr Mladek
parent 35b2b16348
commit 636babdc06
1 changed files with 37 additions and 4 deletions
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41
kernel/printk/printk.c
View file

@ -390,8 +390,12 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
printk_safe_exit_irqrestore(flags); \
} while (0)
/* syslog_lock protects syslog_* variables and write access to clear_seq. */
static DEFINE_RAW_SPINLOCK(syslog_lock);
#ifdef CONFIG_PRINTK
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* All 3 protected by @syslog_lock. */
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static size_t syslog_partial;
@ -410,7 +414,7 @@ struct latched_seq {
/*
* The next printk record to read after the last 'clear' command. There are
* two copies (updated with seqcount_latch) so that reads can locklessly
* access a valid value. Writers are synchronized by @logbuf_lock.
* access a valid value. Writers are synchronized by @syslog_lock.
*/
static struct latched_seq clear_seq = {
.latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
@ -470,7 +474,7 @@ bool printk_percpu_data_ready(void)
return __printk_percpu_data_ready;
}
/* Must be called under logbuf_lock. */
/* Must be called under syslog_lock. */
static void latched_seq_write(struct latched_seq *ls, u64 val)
{
raw_write_seqcount_latch(&ls->latch);
@ -1529,7 +1533,9 @@ static int syslog_print(char __user *buf, int size)
size_t skip;
logbuf_lock_irq();
raw_spin_lock(&syslog_lock);
if (!prb_read_valid(prb, syslog_seq, &r)) {
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irq();
break;
}
@ -1559,6 +1565,7 @@ static int syslog_print(char __user *buf, int size)
syslog_partial += n;
} else
n = 0;
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irq();
if (!n)
@ -1625,8 +1632,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
break;
}
if (clear)
if (clear) {
raw_spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, seq);
raw_spin_unlock(&syslog_lock);
}
logbuf_unlock_irq();
kfree(text);
@ -1636,10 +1646,24 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
static void syslog_clear(void)
{
logbuf_lock_irq();
raw_spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, prb_next_seq(prb));
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irq();
}
/* Return a consistent copy of @syslog_seq. */
static u64 read_syslog_seq_irq(void)
{
u64 seq;
raw_spin_lock_irq(&syslog_lock);
seq = syslog_seq;
raw_spin_unlock_irq(&syslog_lock);
return seq;
}
int do_syslog(int type, char __user *buf, int len, int source)
{
struct printk_info info;
@ -1663,8 +1687,9 @@ int do_syslog(int type, char __user *buf, int len, int source)
return 0;
if (!access_ok(buf, len))
return -EFAULT;
error = wait_event_interruptible(log_wait,
prb_read_valid(prb, syslog_seq, NULL));
prb_read_valid(prb, read_syslog_seq_irq(), NULL));
if (error)
return error;
error = syslog_print(buf, len);
@ -1713,8 +1738,10 @@ int do_syslog(int type, char __user *buf, int len, int source)
/* Number of chars in the log buffer */
case SYSLOG_ACTION_SIZE_UNREAD:
logbuf_lock_irq();
raw_spin_lock(&syslog_lock);
if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
/* No unread messages. */
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irq();
return 0;
}
@ -1743,6 +1770,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
}
error -= syslog_partial;
}
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irq();
break;
/* Size of the log buffer */
@ -2992,7 +3020,12 @@ void register_console(struct console *newcon)
*/
exclusive_console = newcon;
exclusive_console_stop_seq = console_seq;
/* Get a consistent copy of @syslog_seq. */
raw_spin_lock(&syslog_lock);
console_seq = syslog_seq;
raw_spin_unlock(&syslog_lock);
logbuf_unlock_irqrestore(flags);
}
console_unlock();