linux-kernel - Re: [PATCH] libnvdimm: fix btt vs clear poison locking

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Message-ID: <x49r30yg116.fsf@segfault.boston.devel.redhat.com>
Date:   Tue, 11 Apr 2017 16:08:37 -0400
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] libnvdimm: fix btt vs clear poison locking

Dan Williams <dan.j.williams@...el.com> writes:

> As a minimal fix, disable error clearing when the BTT is enabled. For
> the final fix a larger rework of the poison list locking is needed.

> @@ -243,7 +243,15 @@ static int nsio_rw_bytes(struct nd_namespace_common *ndns,
>  	}
>  
>  	if (unlikely(is_bad_pmem(&nsio->bb, sector, sz_align))) {
> -		if (IS_ALIGNED(offset, 512) && IS_ALIGNED(size, 512)) {
> +		/*
> +		 * FIXME: nsio_rw_bytes() may be called from atomic
> +		 * context in the BTT case and nvdimm_clear_poison()
> +		 * takes a sleeping lock. Until the locking can be
> +		 * reworked this capability depends on !BTT or BROKEN.
> +		 */
> +		if ((!IS_ENABLED(CONFIG_BTT) || IS_ENABLED(CONFIG_BROKEN))
> +				&& IS_ALIGNED(offset, 512)
> +				&& IS_ALIGNED(size, 512)) {

I don't like that you've disabled clear error just because the btt
driver was enabled.  Can't you do something like this, instead?

	disable_clear_poison = (ndns->claim && is_nd_btt(ndns->claim));

	if (!disable_clear_poison && IS_ALIGNED(offset, 512)...

-Jeff