lkml.org 
[lkml]   [2022]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] net: ocelot: fix wront time_after usage
From
Hi Andrew,

On 5/20/22 15:40, Andrew Lunn wrote:
> 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.
>

I wasn't aware about these macros. Thanks for pointing out to that header!

Will send v2 soon,



With regards,
Pavel Skripkin
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2022-05-20 23:07    [W:0.081 / U:0.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site