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.
Signed-off-by: John Ogness <[email protected]> --- kernel/printk/printk.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index fe3df16315c0..506d334c065e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -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), @@ -465,7 +469,7 @@ 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); @@ -1515,7 +1519,9 @@ 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; } @@ -1545,6 +1551,7 @@ 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) @@ -1611,8 +1618,11 @@ 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); @@ -1622,7 +1632,9 @@ 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(); } @@ -1631,6 +1643,7 @@ int do_syslog(int type, char __user *buf, int len, int source) bool clear = false; static int saved_console_loglevel = LOGLEVEL_DEFAULT; int error; + u64 seq; error = check_syslog_permissions(type, source); if (error) @@ -1648,8 +1661,14 @@ int do_syslog(int type, char __user *buf, int len, int source) return 0; if (!access_ok(buf, len)) return -EFAULT; + + /* Get a consistent copy of @syslog_seq. */ + raw_spin_lock_irq(&syslog_lock); + seq = syslog_seq; + raw_spin_unlock_irq(&syslog_lock); + error = wait_event_interruptible(log_wait, - prb_read_valid(prb, syslog_seq, NULL)); + prb_read_valid(prb, seq, NULL)); if (error) return error; error = syslog_print(buf, len); @@ -1698,6 +1717,7 @@ 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 (syslog_seq < prb_first_valid_seq(prb)) { /* messages are gone, move to first one */ syslog_seq = prb_first_valid_seq(prb); @@ -1724,6 +1744,7 @@ 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 */ @@ -2965,7 +2986,12 @@ 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(); -- 2.20.1
