linux-kernel - Re: [PATCH 1/2] bcachefs: do not use PF_MEMALLOC

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Message-ID: <Zszado75SnObVKG5@casper.infradead.org>
Date: Mon, 26 Aug 2024 20:41:42 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Yafang Shao <laoar.shao@...il.com>,
	jack@...e.cz, Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-bcachefs@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 1/2] bcachefs: do not use PF_MEMALLOC_NORECLAIM

On Mon, Aug 26, 2024 at 03:39:47PM -0400, Kent Overstreet wrote:
> Given the amount of plumbing required here, it's clear that passing gfp
> flags is the less safe way of doing it, and this really does belong in
> the allocation context.
> 
> Failure to pass gfp flags correctly (which we know is something that
> happens today, e.g. vmalloc -> pte allocation) means you're introducing
> a deadlock.

The problem with vmalloc is that the page table allocation _doesn't_
take a GFP parameter.