linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: bio

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Message-ID: <20191030163313.GB34056@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Wed, 30 Oct 2019 09:33:13 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Gao Xiang <hsiangkao@....com>, Gao Xiang <gaoxiang25@...wei.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: bio_alloc should never fail

On 10/30, Theodore Y. Ts'o wrote:
> On Wed, Oct 30, 2019 at 11:50:37PM +0800, Gao Xiang wrote:
> > 
> > So I'm curious about the original issue in commit 740432f83560
> > ("f2fs: handle failed bio allocation"). Since f2fs manages multiple write
> > bios with its internal fio but it seems the commit is not helpful to
> > resolve potential mempool deadlock (I'm confused since no calltrace,
> > maybe I'm wrong)...
> 
> Two possibilities come to mind.  (a) It may be that on older kernels
> (when f2fs is backported to older Board Support Package kernels from
> the SOC vendors) didn't have the bio_alloc() guarantee, so it was
> necessary on older kernels, but not on upstream, or (b) it wasn't
> *actually* possible for bio_alloc() to fail and someone added the
> error handling in 740432f83560 out of paranoia.

Yup, I was checking old device kernels but just stopped digging it out.
Instead, I hesitate to apply this patch since I can't get why we need to
get rid of this code for clean-up purpose. This may be able to bring
some hassles when backporting to android/device kernels.

> 
> (Hence my suggestion that in the ext4 version of the patch, we add a
> code comment justifying why there was no error checking, to make it
> clear that this was a deliberate choice.  :-)
> 
> 						- Ted