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    SubjectRe: [PATCH printk-rework 07/14] printk: use atomic64_t for devkmsg_user.seq
    On Thu 2021-02-18 09:18:10, John Ogness wrote:
    > @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 a71e0d41ccb5..20c21a25143d 100644
    > --- a/kernel/printk/printk.c
    > +++ b/kernel/printk/printk.c
    > @@ -865,9 +865,9 @@ 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(prb, atomic64_read(&user->seq), NULL)) {

    s/prb_read_valid/prb_read_valid_info/

    It is likely a mistake when rebasing on top of the commit
    13791c80b0cdf54d ("printk: avoid prb_first_valid_seq() where possible").

    > /* 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;

    With the above fix:

    Reviewed-by: Petr Mladek <pmladek@suse.com>

    Best Regards,
    Petr

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