Messages in this thread | | | Date | Fri, 20 May 2022 14:40:59 +0200 | From | Andrew Lunn <> | Subject | Re: [PATCH] net: ocelot: fix wront time_after usage |
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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
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