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153 lines
4.5 KiB
Diff
153 lines
4.5 KiB
Diff
From: John Ogness <john.ogness@linutronix.de>
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Date: Thu, 10 Dec 2020 16:58:02 +0106
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Subject: [PATCH 09/28] printk: add syslog_lock
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The global variables @syslog_seq, @syslog_partial, @syslog_time
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and write access to @clear_seq are protected by @logbuf_lock.
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Once @logbuf_lock is removed, these variables will need their
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own synchronization method. Introduce @syslog_lock for this
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purpose.
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@syslog_lock is a raw_spin_lock for now. This simplifies the
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transition to removing @logbuf_lock. Once @logbuf_lock and the
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safe buffers are removed, @syslog_lock can change to spin_lock.
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++++++++++----
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1 file changed, 37 insertions(+), 4 deletions(-)
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -390,8 +390,12 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
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printk_safe_exit_irqrestore(flags); \
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} while (0)
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+/* syslog_lock protects syslog_* variables and write access to clear_seq. */
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+static DEFINE_RAW_SPINLOCK(syslog_lock);
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+
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#ifdef CONFIG_PRINTK
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DECLARE_WAIT_QUEUE_HEAD(log_wait);
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+/* All 3 protected by @syslog_lock. */
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/* the next printk record to read by syslog(READ) or /proc/kmsg */
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static u64 syslog_seq;
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static size_t syslog_partial;
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@@ -410,7 +414,7 @@ struct latched_seq {
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/*
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* The next printk record to read after the last 'clear' command. There are
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* two copies (updated with seqcount_latch) so that reads can locklessly
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- * access a valid value. Writers are synchronized by @logbuf_lock.
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+ * access a valid value. Writers are synchronized by @syslog_lock.
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*/
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static struct latched_seq clear_seq = {
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.latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
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@@ -470,7 +474,7 @@ bool printk_percpu_data_ready(void)
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return __printk_percpu_data_ready;
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}
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-/* Must be called under logbuf_lock. */
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+/* Must be called under syslog_lock. */
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static void latched_seq_write(struct latched_seq *ls, u64 val)
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{
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raw_write_seqcount_latch(&ls->latch);
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@@ -1529,7 +1533,9 @@ static int syslog_print(char __user *buf
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size_t skip;
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logbuf_lock_irq();
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+ raw_spin_lock(&syslog_lock);
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if (!prb_read_valid(prb, syslog_seq, &r)) {
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+ raw_spin_unlock(&syslog_lock);
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logbuf_unlock_irq();
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break;
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}
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@@ -1559,6 +1565,7 @@ static int syslog_print(char __user *buf
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syslog_partial += n;
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} else
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n = 0;
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+ raw_spin_unlock(&syslog_lock);
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logbuf_unlock_irq();
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if (!n)
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@@ -1625,8 +1632,11 @@ static int syslog_print_all(char __user
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break;
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}
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- if (clear)
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+ if (clear) {
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+ raw_spin_lock(&syslog_lock);
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latched_seq_write(&clear_seq, seq);
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+ raw_spin_unlock(&syslog_lock);
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+ }
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logbuf_unlock_irq();
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kfree(text);
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@@ -1636,10 +1646,24 @@ static int syslog_print_all(char __user
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static void syslog_clear(void)
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{
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logbuf_lock_irq();
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+ raw_spin_lock(&syslog_lock);
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latched_seq_write(&clear_seq, prb_next_seq(prb));
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+ raw_spin_unlock(&syslog_lock);
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logbuf_unlock_irq();
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}
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+/* Return a consistent copy of @syslog_seq. */
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+static u64 read_syslog_seq_irq(void)
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+{
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+ u64 seq;
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+
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+ raw_spin_lock_irq(&syslog_lock);
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+ seq = syslog_seq;
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+ raw_spin_unlock_irq(&syslog_lock);
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+
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+ return seq;
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+}
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+
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int do_syslog(int type, char __user *buf, int len, int source)
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{
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struct printk_info info;
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@@ -1663,8 +1687,9 @@ int do_syslog(int type, char __user *buf
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return 0;
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if (!access_ok(buf, len))
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return -EFAULT;
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+
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error = wait_event_interruptible(log_wait,
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- prb_read_valid(prb, syslog_seq, NULL));
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+ prb_read_valid(prb, read_syslog_seq_irq(), NULL));
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if (error)
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return error;
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error = syslog_print(buf, len);
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@@ -1713,8 +1738,10 @@ int do_syslog(int type, char __user *buf
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/* Number of chars in the log buffer */
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case SYSLOG_ACTION_SIZE_UNREAD:
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logbuf_lock_irq();
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+ raw_spin_lock(&syslog_lock);
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if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
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/* No unread messages. */
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+ raw_spin_unlock(&syslog_lock);
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logbuf_unlock_irq();
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return 0;
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}
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@@ -1743,6 +1770,7 @@ int do_syslog(int type, char __user *buf
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}
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error -= syslog_partial;
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}
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+ raw_spin_unlock(&syslog_lock);
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logbuf_unlock_irq();
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break;
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/* Size of the log buffer */
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@@ -2992,7 +3020,12 @@ void register_console(struct console *ne
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*/
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exclusive_console = newcon;
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exclusive_console_stop_seq = console_seq;
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+
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+ /* Get a consistent copy of @syslog_seq. */
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+ raw_spin_lock(&syslog_lock);
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console_seq = syslog_seq;
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+ raw_spin_unlock(&syslog_lock);
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+
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logbuf_unlock_irqrestore(flags);
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}
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console_unlock();
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