From 5521ed0e06ffc572d9f0ebf5421ab23288899804 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 10 Dec 2020 16:58:02 +0106 Subject: [PATCH 089/323] printk: add syslog_lock Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz 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 Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++++++++++---- 1 file changed, 37 insertions(+), 4 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index a351ed400c04..986fc9fad210 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -392,8 +392,12 @@ 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; @@ -412,7 +416,7 @@ 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), @@ -472,7 +476,7 @@ 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); @@ -1532,7 +1536,9 @@ 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; } @@ -1562,6 +1568,7 @@ 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) @@ -1628,8 +1635,11 @@ 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); @@ -1639,10 +1649,24 @@ 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; @@ -1666,8 +1690,9 @@ 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); @@ -1716,8 +1741,10 @@ 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; } @@ -1746,6 +1773,7 @@ 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 */ @@ -2995,7 +3023,12 @@ 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(); -- 2.43.0