Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk-rework 06/12] printk: use atomic64_t for devkmsg_user.seq | Date | Tue, 26 Jan 2021 22:21:45 +0106 |
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@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> --- kernel/printk/printk.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index d41fd3306f4e..fe3df16315c0 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -657,7 +657,7 @@ 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]; @@ -759,7 +759,7 @@ 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(); @@ -768,15 +768,15 @@ 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 (user->seq < prb_first_valid_seq(prb)) { + if (atomic64_read(&user->seq) < prb_first_valid_seq(prb)) { /* our last seen message is gone, return error and reset */ - user->seq = prb_first_valid_seq(prb); + atomic64_set(&user->seq, prb_first_valid_seq(prb)); ret = -EPIPE; logbuf_unlock_irq(); goto out; @@ -787,7 +787,7 @@ 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) { @@ -827,7 +827,7 @@ 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: /* @@ -835,11 +835,11 @@ 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; @@ -859,9 +859,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait) poll_wait(file, &log_wait, wait); logbuf_lock_irq(); - if (prb_read_valid(prb, user->seq, NULL)) { + if (prb_read_valid(prb, atomic64_read(&user->seq), NULL)) { /* return error when data has vanished underneath us */ - if (user->seq < prb_first_valid_seq(prb)) + if (atomic64_read(&user->seq) < prb_first_valid_seq(prb)) ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI; else ret = EPOLLIN|EPOLLRDNORM; @@ -900,7 +900,7 @@ 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; -- 2.20.1
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