linux-kernel - Re: [PATCH AUTOSEL 4.19 059/206] ext4: make dioread

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Message-ID: <20200918171858.GA80112@mit.edu>
Date:   Fri, 18 Sep 2020 13:18:58 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 059/206] ext4: make dioread_nolock the
 default

On Thu, Sep 17, 2020 at 07:58:59PM -0700, Eric Biggers wrote:
> On Thu, Sep 17, 2020 at 10:05:35PM -0400, Sasha Levin wrote:
> > From: Theodore Ts'o <tytso@....edu>
> > 
> > [ Upstream commit 244adf6426ee31a83f397b700d964cff12a247d3 ]
> > 
> > This fixes the direct I/O versus writeback race which can reveal stale
> > data, and it improves the tail latency of commits on slow devices.
> > 
> > Link: https://lore.kernel.org/r/20200125022254.1101588-1-tytso@mit.edu
> > Signed-off-by: Theodore Ts'o <tytso@....edu>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>I
> 
> Any particular reason to be backporting this?  I thought I saw some fixes for
> dioread_nolock go by, after it was made the default.  Are you getting all of
> those fixes too?

Agreed, making dioread_nolock the default has enough issues that it's
not something that I'd suggest backporting at this point.  It's a
fundamental behavioral change that it's not something we should change
in a stable kernel.

						- Ted