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From: Arul Jeniston <arul.jeniston@gmail.com>
To: viro@zeniv.linux.org.uk, tglx@linutronix.de
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	arul_mc@dell.com, ARUL JENISTON MC <arul.jeniston@gmail.com>
Subject: [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function.
Date: Fri, 16 Aug 2019 15:52:09 +0530
Message-ID: <CACAVd4iXVH2U41msVKhT4GBGgE=2V2oXnOXkQUQKSSh72HMMmw@mail.gmail.com> (raw)
In-Reply-To: <20190816083246.169312-1-arul.jeniston@gmail.com>

'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
. This patch fixes this problem.
Signed-off-by: Arul Jeniston <arul.jeniston@gmail.com>


---
 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);
+                               /*
+                                * ticks shouldn't become zero at this point.
+                                * Ignore if hrtimer_forward_now returns 0
+                                * due to larger backward time drift.
+                                */
+                               if (likely(nooftimeo)) {
+                                       ticks += nooftimeo - 1;
+                               }
                                hrtimer_restart(&ctx->t.tmr);
                        }
                }
--
2.11.0

  parent reply index

Thread overview: 17+ 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 ` Arul Jeniston [this message]
2019-08-16 10:45   ` [PATCH] FS: timerfd: Fix unexpected return value of timerfd_read function Thomas Gleixner
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
     [not found]                               ` <CACAVd4jAJ5QcOH=q=Q9kAz20X4_nAc7=vVU_gPWTS1UuiGK-fg@mail.gmail.com>
2019-08-20  8:49                                 ` Thomas Gleixner
2019-08-20  9:42                                   ` Arul Jeniston

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