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Date:   Tue, 11 Oct 2022 17:00:57 +0200
From:   Guillaume Nault <gnault@redhat.com>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna@kernel.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>, linux-nfs@vger.kernel.org,
        Paolo Abeni <pabeni@redhat.com>,
        Benjamin Coddington <bcodding@redhat.com>
Subject: Re: [PATCH v2] sunrpc: Use GFP_NOFS to prevent use of
 current->task_frag.
Message-ID: <20221011150057.GB3606@localhost.localdomain>
References: <de6d99321d1dcaa2ad456b92b3680aa77c07a747.1665401788.git.gnault@redhat.com>
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 <20221010165650.GA3456@ibm-p9z-18-fsp.mgmt.pnr.lab.eng.rdu2.redhat.com>
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On Mon, Oct 10, 2022 at 11:18:19PM -0700, Christoph Hellwig wrote:
> On Mon, Oct 10, 2022 at 06:56:50PM +0200, Guillaume Nault wrote:
> > That's what my RFC patch did. It was rejected because reading
> > current->flags may incur a cache miss thus slowing down TCP fast path.
> > See the discussion in the Link tag:
> > https://lore.kernel.org/netdev/b4d8cb09c913d3e34f853736f3f5628abfd7f4b6.1656699567.git.gnault@redhat.com/
> 
> As GFP_NOFS/NOIO are on their way out the networking people will have to
> do this anyway.

We can always think of a nicer solution in the future. But right now we
have a real bug to fix.

Commit a1231fda7e94 ("SUNRPC: Set memalloc_nofs_save() on all
rpciod/xprtiod jobs") introduces a bug that crashes the kernel. I can't
see anything wrong with a partial revert.