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Date: Mon, 22 Jan 2024 07:50:38 +0100
From: Christoph Hellwig <hch@lst.de>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Christoph Hellwig <hch@lst.de>, bfoster@redhat.com,
	linux-bcachefs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] bcachefs: fix incorrect usage of REQ_OP_FLUSH
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References: <20240111073655.2095423-1-hch@lst.de> <ueeqal442uw77vrmonr5crix5jehetzg266725shaqi2oim6h7@4q4tlcm2y6k7> <20240122063007.GA23991@lst.de> <eyyg26ls45xqdyjrvowm7hfusfr7ezr3pjve6ojikg4znys6dx@rd2ugzmo44r4>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Jan 22, 2024 at 01:37:45AM -0500, Kent Overstreet wrote:
> > Without this patch as in current mainline you will get -EOPNOTSUPP
> > because sending REQ_OP_FLUSH and finally check for that to catch bugs
> > like the one fixed with this patch.
> 
> Then why did the user report -EOPNOTSUPP with the patch, which went away
> when reverted?

I have no idea, as we never return -EOPNOTSUPP for
REQ_OP_WRITE | REQ_PREFLUSH this would be odd.  According to your
report the users runs a Fedora kernel and this commit never went
upstream or even into linux-next, which doesn't quite add a up to me
either.

But in the end just try it yourself.  On current mainline with the buggy
REQ_OP_FLUSH you should be seeing -EOPNOTSUPP every single time you
try a data integrity operation, without it you should not.  Even the most
basic test should be catching this.