From: Thomas Gleixner <tglx@linutronix.de>
To: Arul Jeniston <arul.jeniston@gmail.com>
Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, arul_mc@dell.com
Subject: Re: [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function.
Date: Fri, 16 Aug 2019 12:45:39 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1908161224220.1873@nanos.tec.linutronix.de> (raw)
In-Reply-To: <CACAVd4iXVH2U41msVKhT4GBGgE=2V2oXnOXkQUQKSSh72HMMmw@mail.gmail.com>
Arul,
On Fri, 16 Aug 2019, Arul Jeniston wrote:
> Subject: [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function.
The prefix is not 'FS: timerfd:'
1) The usual prefix for fs/* is: 'fs:' but...
2) git log fs/timerfd.c gives you a pretty good hint for the proper
prefix. Look at the commits which actually do functional changes to that
file, not at those which do (sub)system wide cleanups/adjustments.
Also 'timerfd_read function' can be written as 'timerfd_read()' which
spares the redundant function and clearly marks it as function via the
brackets.
> 'hrtimer_forward_now()' returns zero due to bigger backward time drift.
> This causes timerfd_read to return 0. As per man page, read on timerfd
> is not expected to return 0.
> This problem is well explained in https://lkml.org/lkml/2019/7/31/442
1) The explanation needs to be in the changelog itself. Links can point to
discussions, bug-reports which have supplementary information.
2) Please do not use lkml.org links.
Again: Please read and follow Documentation/process/submitting-patches.rst
> . This patch fixes this problem.
> Signed-off-by: Arul Jeniston <arul.jeniston@gmail.com>
Missing empty line before Signed-off-by. Please use git-log to see how
changelogs are properly formatted.
Also: 'This patch fixes this problem' is not helpful at all. Again see the
document I already pointed you to.
> ---
> fs/timerfd.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/timerfd.c b/fs/timerfd.c
> index 6a6fc8aa1de7..f5094e070e9a 100644
> --- a/fs/timerfd.c
> +++ b/fs/timerfd.c
> @@ -284,8 +284,16 @@ static ssize_t timerfd_read(struct file *file,
> char __user *buf, size_t count,
> &ctx->t.alarm, ctx->tintv) - 1;
> alarm_restart(&ctx->t.alarm);
> } else {
> - ticks += hrtimer_forward_now(&ctx->t.tmr,
> - ctx->tintv) - 1;
> + u64 nooftimeo = hrtimer_forward_now(&ctx->t.tmr,
> + ctx->tintv);
nooftimeo is pretty non-intuitive. The function documentation of
hrtimer_forward_now() says:
Returns the number of overruns.
So the obvious variable name is overruns, right?
> + /*
> + * ticks shouldn't become zero at this point.
> + * Ignore if hrtimer_forward_now returns 0
> + * due to larger backward time drift.
Again. This explanation does not make any sense at all.
Time does not go backwards, except if it is CLOCK_REALTIME which can be set
backwards via clock_settime() or settimeofday().
> + */
> + if (likely(nooftimeo)) {
> + ticks += nooftimeo - 1;
> + }
Again: Pointless brackets.
If you disagree with my review comment, then tell me in a reply. If not,
then fix it. If you decide to ignore my comments, then don't wonder if I
ignore your patches.
Thanks,
tglx
next prev parent reply other threads:[~2019-08-16 10:45 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-16 8:32 [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function. 'hrtimer_forward_now()' returns zero due to bigger backward time drift. This causes timerfd_read to return 0. As per man page, read on timerfd is not expected to return 0. This patch fixes this problem. Signed-off-by: Arul Jeniston <arul.jeniston@gmail.com> arul.jeniston
2019-08-16 9:05 ` [PATCH] FS: timerfd: [Trimmed unreadable long subject line ] Thomas Gleixner
2019-08-16 10:22 ` [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function Arul Jeniston
2019-08-16 10:45 ` Thomas Gleixner [this message]
2019-08-16 16:55 ` Arul Jeniston
2019-08-16 17:00 ` Arul Jeniston
2019-08-16 21:17 ` Thomas Gleixner
[not found] ` <CACAVd4hT6QYtgtDsBcgy7c_s9WVBAH+1m0r5geBe7BUWJWYhbA@mail.gmail.com>
2019-08-17 19:23 ` Thomas Gleixner
2019-08-19 6:07 ` Arul Jeniston
2019-08-19 8:04 ` Thomas Gleixner
2019-08-19 14:25 ` Arul Jeniston
2019-08-19 14:52 ` Thomas Gleixner
2019-08-19 15:26 ` Arul Jeniston
2019-08-19 15:59 ` Thomas Gleixner
[not found] ` <CACAVd4iRN7=eq_B1+Yb-xcspU-Sg1dmMo_=VtLXXVPkjN1hY5Q@mail.gmail.com>
2019-08-19 18:29 ` Thomas Gleixner
2019-08-20 6:11 ` Arul Jeniston
2019-08-20 8:49 ` Thomas Gleixner
2019-08-20 9:42 ` Arul Jeniston
2019-09-05 8:48 ` Arul Jeniston
2019-09-05 15:34 ` Thomas Gleixner
2019-09-06 16:36 ` Arul Jeniston
2019-09-07 14:38 ` Thomas Gleixner
2019-11-05 5:01 ` Arul Jeniston
2019-11-05 10:01 ` Thomas Gleixner
2019-11-06 3:38 ` Arul Jeniston
2020-02-12 18:14 ` Arul Jeniston
2020-02-13 12:11 ` Thomas Gleixner
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