lkml.org 
[lkml]   [2022]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] net: ocelot: fix wront time_after usage
On Thu, May 19, 2022 at 11:40:17PM +0300, Pavel Skripkin wrote:
> Accidentally noticed, that this driver is the only user of
> while (timer_after(jiffies...)).
>
> It looks like typo, because likely this while loop will finish after 1st
> iteration, because time_after() returns true when 1st argument _is after_
> 2nd one.
>
> Fix it by negating time_after return value inside while loops statement

A better fix would be to use one of the helpers in linux/iopoll.h.

There is a second bug in the current code:

static int ocelot_fdma_wait_chan_safe(struct ocelot *ocelot, int chan)
{
unsigned long timeout;
u32 safe;

timeout = jiffies + usecs_to_jiffies(OCELOT_FDMA_CH_SAFE_TIMEOUT_US);
do {
safe = ocelot_fdma_readl(ocelot, MSCC_FDMA_CH_SAFE);
if (safe & BIT(chan))
return 0;
} while (time_after(jiffies, timeout));

return -ETIMEDOUT;
}

The scheduler could put the thread to sleep, and it does not get woken
up for OCELOT_FDMA_CH_SAFE_TIMEOUT_US. During that time, the hardware
has done its thing, but you exit the while loop and return -ETIMEDOUT.

linux/iopoll.h handles this correctly by testing the state one more
time after the timeout has expired.

Andrew

\
 
 \ /
  Last update: 2022-05-20 14:42    [W:0.124 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site