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Subject[PATCH next v2 2/3] printk: change @clear_seq to atomic64_t
Date
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 <john.ogness@linutronix.de>
---
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
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