Messages in this thread | | | Date | Fri, 4 Dec 2020 16:52:35 +0100 | From | Petr Mladek <> | Subject | devkmsg: was [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock |
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On Tue 2020-12-01 21:59:41, John Ogness wrote: > Since the ringbuffer is lockless, there is no need for it to be > protected by @logbuf_lock. Remove @logbuf_lock.
I am going to split the feedback into few mails. It might make sense to split also this patch into few more pieces that would remove the lock from a particular interface.
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index e9018c4e1b66..7385101210be 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -785,7 +749,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) > if (offset) > return -ESPIPE; > > - logbuf_lock_irq();
user->seq manipulation is not longer safe from the atomicity point of view.
One solution would be to use atomic variable in struct devkmsg_user(). Another solution would be to synchronize it with user->lock like we do in devkmsg_read().
user->lock looks like an overhead. But it actually would make sense to prevent seek in the middle of a read.
> switch (whence) { > case SEEK_SET: > /* the first record */ > @@ -820,7 +782,6 @@ 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)) {
Same here. The atomicity of user->seq read/write is not guaranteed.
> /* return error when data has vanished underneath us */ > if (user->seq < prb_first_valid_seq(prb))
Best Regards, Petr
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