linux-kernel - Re: [PATCH] mtd: nand: check status before reporting timeout

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Message-ID: <20160307215140.GB55664@google.com>
Date:	Mon, 7 Mar 2016 13:51:40 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	linux-mtd@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Richard Weinberger <richard@....at>,
	Harvey Hunt <harvey.hunt@...tec.com>,
	Alex Smith <alex.smith@...tec.com>,
	Niklas Cassel <niklas.cassel@...s.com>,
	Alex Smith <alex@...x-smith.me.uk>
Subject: Re: [PATCH] mtd: nand: check status before reporting timeout

On Fri, Mar 04, 2016 at 05:19:23PM -0800, Brian Norris wrote:
> In commit b70af9bef49b ("mtd: nand: increase ready wait timeout and
> report timeouts"), we increased the likelihood of scheduling during
> nand_wait(). This makes us more likely to hit the time_before(...)
> condition, since a lot of time may pass before we get scheduled again.
> 
> Now, the loop was already buggy, since we don't check if the NAND is
> ready after exiting the loop; we simply print out a timeout warning. Fix
> this by doing a final status check before printing a timeout message.
> 
> This isn't actually a critical bug, since the only effect is a false
> warning print. But too many prints never hurt anyone, did they? :)
> 
> Side note: perhaps I'm not smart enough, but I'm not sure what the best
> policy is for this kind of loop; do we busy loop (i.e., no
> cond_resched()) to keep the lowest I/O latency (it's not great if the
> resched is delaying Richard's system ~400ms)? Or do we allow
> rescheduling, to play nice with the rest of the system (since some
> operations can take quite a while)?
> 
> Reported-by: Richard Weinberger <richard@....at>
> Signed-off-by: Brian Norris <computersforpeace@...il.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Reviewed-by: Richard Weinberger <richard@....at>
> Reviewed-by: Harvey Hunt <harvey.hunt@...tec.com>

Applied