printk: remove logbuf_lock

Since the ringbuffer is lockless, there is no need for it to be
protected by @logbuf_lock. Remove @logbuf_lock.

@console_seq, @exclusive_console_stop_seq, @console_dropped are
protected by @console_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/20210303101528.29901-14-john.ogness@linutronix.de

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 3a8fd49..e7acc28 100644 (file)
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -12,8 +12,6 @@
 
 #define PRINTK_NMI_CONTEXT_OFFSET      0x010000000
 
-extern raw_spinlock_t logbuf_lock;
-
 __printf(4, 0)
 int vprintk_store(int facility, int level,
                  const struct dev_printk_info *dev_info,
@@ -59,7 +57,7 @@ void defer_console_output(void);
 __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
+ * In !PRINTK builds we still export console_sem
  * semaphore and some of console functions (console_unlock()/etc.), so
  * printk-safe must preserve the existing local IRQ guarantees.
  */

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index b49dee2..8994bc1 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -355,41 +355,6 @@ enum log_flags {
        LOG_CONT        = 8,    /* text is a fragment of a continuation line */
 };
 
-/*
- * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
- * within the scheduler's rq lock. It must be released before calling
- * console_unlock() or anything else that might wake up a process.
- */
-DEFINE_RAW_SPINLOCK(logbuf_lock);
-
-/*
- * Helper macros to lock/unlock logbuf_lock and switch between
- * printk-safe/unsafe modes.
- */
-#define logbuf_lock_irq()                              \
-       do {                                            \
-               printk_safe_enter_irq();                \
-               raw_spin_lock(&logbuf_lock);            \
-       } while (0)
-
-#define logbuf_unlock_irq()                            \
-       do {                                            \
-               raw_spin_unlock(&logbuf_lock);          \
-               printk_safe_exit_irq();                 \
-       } while (0)
-
-#define logbuf_lock_irqsave(flags)                     \
-       do {                                            \
-               printk_safe_enter_irqsave(flags);       \
-               raw_spin_lock(&logbuf_lock);            \
-       } while (0)
-
-#define logbuf_unlock_irqrestore(flags)                \
-       do {                                            \
-               raw_spin_unlock(&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);
 
@@ -401,6 +366,7 @@ static u64 syslog_seq;
 static size_t syslog_partial;
 static bool syslog_time;
 
+/* All 3 protected by @console_sem. */
 /* the next printk record to write to the console */
 static u64 console_seq;
 static u64 exclusive_console_stop_seq;
@@ -766,27 +732,27 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
        if (ret)
                return ret;
 
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
                if (file->f_flags & O_NONBLOCK) {
                        ret = -EAGAIN;
-                       logbuf_unlock_irq();
+                       printk_safe_exit_irq();
                        goto out;
                }
 
-               logbuf_unlock_irq();
+               printk_safe_exit_irq();
                ret = wait_event_interruptible(log_wait,
                                prb_read_valid(prb, atomic64_read(&user->seq), r));
                if (ret)
                        goto out;
-               logbuf_lock_irq();
+               printk_safe_enter_irq();
        }
 
        if (r->info->seq != atomic64_read(&user->seq)) {
                /* our last seen message is gone, return error and reset */
                atomic64_set(&user->seq, r->info->seq);
                ret = -EPIPE;
-               logbuf_unlock_irq();
+               printk_safe_exit_irq();
                goto out;
        }
 
@@ -796,7 +762,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
                                  &r->info->dev_info);
 
        atomic64_set(&user->seq, r->info->seq + 1);
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
 
        if (len > count) {
                ret = -EINVAL;
@@ -831,7 +797,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
        if (offset)
                return -ESPIPE;
 
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        switch (whence) {
        case SEEK_SET:
                /* the first record */
@@ -852,7 +818,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
        default:
                ret = -EINVAL;
        }
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
        return ret;
 }
 
@@ -867,7 +833,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 
        poll_wait(file, &log_wait, wait);
 
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
                /* return error when data has vanished underneath us */
                if (info.seq != atomic64_read(&user->seq))
@@ -875,7 +841,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
                else
                        ret = EPOLLIN|EPOLLRDNORM;
        }
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
 
        return ret;
 }
@@ -908,9 +874,9 @@ static int devkmsg_open(struct inode *inode, struct file *file)
        prb_rec_init_rd(&user->record, &user->info,
                        &user->text_buf[0], sizeof(user->text_buf));
 
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        atomic64_set(&user->seq, prb_first_valid_seq(prb));
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
 
        file->private_data = user;
        return 0;
@@ -1532,11 +1498,11 @@ static int syslog_print(char __user *buf, int size)
                size_t n;
                size_t skip;
 
-               logbuf_lock_irq();
+               printk_safe_enter_irq();
                raw_spin_lock(&syslog_lock);
                if (!prb_read_valid(prb, syslog_seq, &r)) {
                        raw_spin_unlock(&syslog_lock);
-                       logbuf_unlock_irq();
+                       printk_safe_exit_irq();
                        break;
                }
                if (r.info->seq != syslog_seq) {
@@ -1566,7 +1532,7 @@ static int syslog_print(char __user *buf, int size)
                } else
                        n = 0;
                raw_spin_unlock(&syslog_lock);
-               logbuf_unlock_irq();
+               printk_safe_exit_irq();
 
                if (!n)
                        break;
@@ -1600,7 +1566,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                return -ENOMEM;
 
        time = printk_time;
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        /*
         * Find first record that fits, including all following records,
         * into the user-provided buffer for this dump.
@@ -1621,12 +1587,12 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                        break;
                }
 
-               logbuf_unlock_irq();
+               printk_safe_exit_irq();
                if (copy_to_user(buf + len, text, textlen))
                        len = -EFAULT;
                else
                        len += textlen;
-               logbuf_lock_irq();
+               printk_safe_enter_irq();
 
                if (len < 0)
                        break;
@@ -1637,7 +1603,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
                latched_seq_write(&clear_seq, seq);
                raw_spin_unlock(&syslog_lock);
        }
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
 
        kfree(text);
        return len;
@@ -1645,11 +1611,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 
 static void syslog_clear(void)
 {
-       logbuf_lock_irq();
+       printk_safe_enter_irq();
        raw_spin_lock(&syslog_lock);
        latched_seq_write(&clear_seq, prb_next_seq(prb));
        raw_spin_unlock(&syslog_lock);
-       logbuf_unlock_irq();
+       printk_safe_exit_irq();
 }
 
 /* Return a consistent copy of @syslog_seq. */
@@ -1737,12 +1703,12 @@ int do_syslog(int type, char __user *buf, int len, int source)
                break;
        /* Number of chars in the log buffer */
        case SYSLOG_ACTION_SIZE_UNREAD:
-               logbuf_lock_irq();
+               printk_safe_enter_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();
+                       printk_safe_exit_irq();
                        return 0;
                }
                if (info.seq != syslog_seq) {
@@ -1771,7 +1737,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
                        error -= syslog_partial;
                }
                raw_spin_unlock(&syslog_lock);
-               logbuf_unlock_irq();
+               printk_safe_exit_irq();
                break;
        /* Size of the log buffer */
        case SYSLOG_ACTION_SIZE_BUFFER:
@@ -2627,7 +2593,6 @@ again:
                size_t len;
 
                printk_safe_enter_irqsave(flags);
-               raw_spin_lock(&logbuf_lock);
 skip:
                if (!prb_read_valid(prb, console_seq, &r))
                        break;
@@ -2671,7 +2636,6 @@ skip:
                                console_msg_format & MSG_FORMAT_SYSLOG,
                                printk_time);
                console_seq++;
-               raw_spin_unlock(&logbuf_lock);
 
                /*
                 * While actively printing out messages, if another printk()
@@ -2698,8 +2662,6 @@ skip:
 
        console_locked = 0;
 
-       raw_spin_unlock(&logbuf_lock);
-
        up_console_sem();
 
        /*
@@ -2708,9 +2670,7 @@ skip:
         * there's a new owner and the console_unlock() from them will do the
         * flush, no worries.
         */
-       raw_spin_lock(&logbuf_lock);
        retry = prb_read_valid(prb, console_seq, NULL);
-       raw_spin_unlock(&logbuf_lock);
        printk_safe_exit_irqrestore(flags);
 
        if (retry && console_trylock())
@@ -2777,9 +2737,9 @@ void console_flush_on_panic(enum con_flush_mode mode)
        if (mode == CONSOLE_REPLAY_ALL) {
                unsigned long flags;
 
-               logbuf_lock_irqsave(flags);
+               printk_safe_enter_irqsave(flags);
                console_seq = prb_first_valid_seq(prb);
-               logbuf_unlock_irqrestore(flags);
+               printk_safe_exit_irqrestore(flags);
        }
        console_unlock();
 }
@@ -3008,7 +2968,7 @@ void register_console(struct console *newcon)
                 * console_unlock(); will print out the buffered messages
                 * for us.
                 */
-               logbuf_lock_irqsave(flags);
+               printk_safe_enter_irqsave(flags);
                /*
                 * We're about to replay the log buffer.  Only do this to the
                 * just-registered console to avoid excessive message spam to
@@ -3026,7 +2986,7 @@ void register_console(struct console *newcon)
                console_seq = syslog_seq;
                raw_spin_unlock(&syslog_lock);
 
-               logbuf_unlock_irqrestore(flags);
+               printk_safe_exit_irqrestore(flags);
        }
        console_unlock();
        console_sysfs_notify();
@@ -3492,9 +3452,9 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
        unsigned long flags;
        bool ret;
 
-       logbuf_lock_irqsave(flags);
+       printk_safe_enter_irqsave(flags);
        ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
-       logbuf_unlock_irqrestore(flags);
+       printk_safe_exit_irqrestore(flags);
 
        return ret;
 }
@@ -3538,7 +3498,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
        if (iter->cur_seq < min_seq)
                iter->cur_seq = min_seq;
 
-       logbuf_lock_irqsave(flags);
+       printk_safe_enter_irqsave(flags);
        if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
                if (info.seq != iter->cur_seq) {
                        /* messages are gone, move to first available one */
@@ -3548,7 +3508,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
        /* last entry */
        if (iter->cur_seq >= iter->next_seq) {
-               logbuf_unlock_irqrestore(flags);
+               printk_safe_exit_irqrestore(flags);
                goto out;
        }
 
@@ -3582,7 +3542,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
        iter->next_seq = next_seq;
        ret = true;
-       logbuf_unlock_irqrestore(flags);
+       printk_safe_exit_irqrestore(flags);
 out:
        if (len_out)
                *len_out = len;
@@ -3618,9 +3578,9 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
        unsigned long flags;
 
-       logbuf_lock_irqsave(flags);
+       printk_safe_enter_irqsave(flags);
        kmsg_dump_rewind_nolock(iter);
-       logbuf_unlock_irqrestore(flags);
+       printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 2e9e3ed..bbf5c19 100644 (file)
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -16,7 +16,7 @@
 #include "internal.h"
 
 /*
- * printk() could not take logbuf_lock in NMI context. Instead,
+ * In NMI and safe mode, printk() avoids taking locks. Instead,
  * it uses an alternative implementation that temporary stores
  * the strings into a per-CPU buffer. The content of the buffer
  * is later flushed into the main ring buffer via IRQ work.
@@ -267,17 +267,9 @@ void printk_safe_flush(void)
 void printk_safe_flush_on_panic(void)
 {
        /*
-        * Make sure that we could access the main ring buffer.
+        * Make sure that we could access the safe buffers.
         * Do not risk a double release when more CPUs are up.
         */
-       if (raw_spin_is_locked(&logbuf_lock)) {
-               if (num_online_cpus() > 1)
-                       return;
-
-               debug_locks_off();
-               raw_spin_lock_init(&logbuf_lock);
-       }
-
        if (raw_spin_is_locked(&safe_read_lock)) {
                if (num_online_cpus() > 1)
                        return;
@@ -319,9 +311,7 @@ void noinstr printk_nmi_exit(void)
  * reordering.
  *
  * It has effect only when called in NMI context. Then printk()
- * will try to store the messages into the main logbuf directly
- * and use the per-CPU buffers only as a fallback when the lock
- * is not available.
+ * will store the messages into the main logbuf directly.
  */
 void printk_nmi_direct_enter(void)
 {
@@ -376,20 +366,21 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
 #endif
 
        /*
-        * Try to use the main logbuf even in NMI. But avoid calling console
+        * Use the main logbuf even in NMI. But avoid calling console
         * drivers that might have their own locks.
         */
-       if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
-           raw_spin_trylock(&logbuf_lock)) {
+       if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK)) {
+               unsigned long flags;
                int len;
 
+               printk_safe_enter_irqsave(flags);
                len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
-               raw_spin_unlock(&logbuf_lock);
+               printk_safe_exit_irqrestore(flags);
                defer_console_output();
                return len;
        }
 
-       /* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
+       /* Use extra buffer in NMI. */
        if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
                return vprintk_nmi(fmt, args);