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printk: use atomic64_t for devkmsg_user.seq 

@user->seq is indirectly protected by @logbuf_lock. Once @logbuf_lock
is removed, @user->seq will be no longer safe from an atomicity point
of view.

In preparation for the removal of @logbuf_lock, change it to
atomic64_t to provide this safety.

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/20210303101528.29901-10-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2021-03-03 11:15:22 +01:00 committed by Petr Mladek
parent 7d7a23a91c
commit 35b2b16348
1 changed files with 12 additions and 12 deletions
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24
kernel/printk/printk.c
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@ -662,7 +662,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
u64 seq;
atomic64_t seq;
struct ratelimit_state rs;
struct mutex lock;
char buf[CONSOLE_EXT_LOG_MAX];
@ -763,7 +763,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
return ret;
logbuf_lock_irq();
if (!prb_read_valid(prb, user->seq, r)) {
if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
logbuf_unlock_irq();
@ -772,15 +772,15 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
logbuf_unlock_irq();
ret = wait_event_interruptible(log_wait,
prb_read_valid(prb, user->seq, r));
prb_read_valid(prb, atomic64_read(&user->seq), r));
if (ret)
goto out;
logbuf_lock_irq();
}
if (r->info->seq != user->seq) {
if (r->info->seq != atomic64_read(&user->seq)) {
/* our last seen message is gone, return error and reset */
user->seq = r->info->seq;
atomic64_set(&user->seq, r->info->seq);
ret = -EPIPE;
logbuf_unlock_irq();
goto out;
@ -791,7 +791,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
&r->text_buf[0], r->info->text_len,
&r->info->dev_info);
user->seq = r->info->seq + 1;
atomic64_set(&user->seq, r->info->seq + 1);
logbuf_unlock_irq();
if (len > count) {
@ -831,7 +831,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
switch (whence) {
case SEEK_SET:
/* the first record */
user->seq = prb_first_valid_seq(prb);
atomic64_set(&user->seq, prb_first_valid_seq(prb));
break;
case SEEK_DATA:
/*
@ -839,11 +839,11 @@ 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 = latched_seq_read_nolock(&clear_seq);
atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
break;
case SEEK_END:
/* after the last record */
user->seq = prb_next_seq(prb);
atomic64_set(&user->seq, prb_next_seq(prb));
break;
default:
ret = -EINVAL;
@ -864,9 +864,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
poll_wait(file, &log_wait, wait);
logbuf_lock_irq();
if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
/* return error when data has vanished underneath us */
if (info.seq != user->seq)
if (info.seq != atomic64_read(&user->seq))
ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
else
ret = EPOLLIN|EPOLLRDNORM;
@ -905,7 +905,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
&user->text_buf[0], sizeof(user->text_buf));
logbuf_lock_irq();
user->seq = prb_first_valid_seq(prb);
atomic64_set(&user->seq, prb_first_valid_seq(prb));
logbuf_unlock_irq();
file->private_data = user;