Currently @clear_seq access is protected by @logbuf_lock. Once @logbuf_lock is removed some other form of synchronization will be required. Change the type of @clear_seq to atomic64_t to provide the synchronization.
Signed-off-by: John Ogness <[email protected]> --- kernel/printk/printk.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index fc5e3a7d6d89..e9018c4e1b66 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -403,7 +403,7 @@ static u64 exclusive_console_stop_seq; static unsigned long console_dropped; /* the next printk record to read after the last 'clear' command */ -static u64 clear_seq; +static atomic64_t clear_seq = ATOMIC64_INIT(0); #ifdef CONFIG_PRINTK_CALLER #define PREFIX_MAX 48 @@ -797,7 +797,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) * like issued by 'dmesg -c'. Reading /dev/kmsg itself * changes no global state, and does not clear anything. */ - user->seq = clear_seq; + user->seq = atomic64_read(&clear_seq); break; case SEEK_END: /* after the last record */ @@ -914,6 +914,9 @@ void log_buf_vmcoreinfo_setup(void) * parse it and detect any changes to structure down the line. */ + VMCOREINFO_SIZE(atomic64_t); + VMCOREINFO_TYPE_OFFSET(atomic64_t, counter); + VMCOREINFO_STRUCT_SIZE(printk_ringbuffer); VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring); VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring); @@ -1476,6 +1479,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear) struct printk_info info; unsigned int line_count; struct printk_record r; + u64 clr_seq; char *text; int len = 0; u64 seq; @@ -1487,15 +1491,17 @@ static int syslog_print_all(char __user *buf, int size, bool clear) time = printk_time; logbuf_lock_irq(); + clr_seq = atomic64_read(&clear_seq); + /* * Find first record that fits, including all following records, * into the user-provided buffer for this dump. */ - prb_for_each_info(clear_seq, prb, seq, &info, &line_count) + prb_for_each_info(clr_seq, prb, seq, &info, &line_count) len += get_record_print_text_size(&info, line_count, true, time); /* move first record forward until length fits into the buffer */ - prb_for_each_info(clear_seq, prb, seq, &info, &line_count) { + prb_for_each_info(clr_seq, prb, seq, &info, &line_count) { if (len <= size) break; len -= get_record_print_text_size(&info, line_count, true, time); @@ -1526,7 +1532,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear) } if (clear) - clear_seq = seq; + atomic64_set(&clear_seq, seq); logbuf_unlock_irq(); kfree(text); @@ -1536,7 +1542,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear) static void syslog_clear(void) { logbuf_lock_irq(); - clear_seq = prb_next_seq(prb); + atomic64_set(&clear_seq, prb_next_seq(prb)); logbuf_unlock_irq(); } @@ -3205,7 +3211,7 @@ void kmsg_dump(enum kmsg_dump_reason reason) dumper->active = true; logbuf_lock_irqsave(flags); - dumper->cur_seq = clear_seq; + dumper->cur_seq = atomic64_read(&clear_seq); dumper->next_seq = prb_next_seq(prb); logbuf_unlock_irqrestore(flags); @@ -3412,7 +3418,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer); */ void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper) { - dumper->cur_seq = clear_seq; + dumper->cur_seq = atomic64_read(&clear_seq); dumper->next_seq = prb_next_seq(prb); } -- 2.20.1
