linux-kernel - [PATCH 2/2] mm: drop PF_MEMALLOC

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Message-ID: <20240826085347.1152675-3-mhocko@kernel.org>
Date: Mon, 26 Aug 2024 10:47:13 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christoph Hellwig <hch@....de>,
	Yafang Shao <laoar.shao@...il.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	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: [PATCH 2/2] mm: drop PF_MEMALLOC_NORECLAIM

From: Michal Hocko <mhocko@...e.com>

There is no existing user of the flag and the flag is dangerous because
a nested allocation context can use GFP_NOFAIL which could cause
unexpected failure. Such a code would be hard to maintain because it
could be deeper in the call chain.

PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
that such a allocation contex is inherently unsafe if the context
doesn't fully control all allocations called from this context.

[1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/sched.h    | 1 -
 include/linux/sched/mm.h | 7 ++-----
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8d150343d42..72dad3a6317a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1657,7 +1657,6 @@ extern struct pid *cad_pid;
 						 * I am cleaning dirty pages from some other bdi. */
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
-#define PF_MEMALLOC_NORECLAIM	0x00800000	/* All allocation requests will clear __GFP_DIRECT_RECLAIM */
 #define PF_MEMALLOC_NOWARN	0x01000000	/* All allocation requests will inherit __GFP_NOWARN */
 #define PF__HOLE__02000000	0x02000000
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 91546493c43d..c49f2b24acb9 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -260,16 +260,13 @@ static inline gfp_t current_gfp_context(gfp_t flags)
 
 	if (unlikely(pflags & (PF_MEMALLOC_NOIO |
 			       PF_MEMALLOC_NOFS |
-			       PF_MEMALLOC_NORECLAIM |
 			       PF_MEMALLOC_NOWARN |
 			       PF_MEMALLOC_PIN))) {
 		/*
 		 * Stronger flags before weaker flags:
-		 * NORECLAIM implies NOIO, which in turn implies NOFS
+		 * NOIO implies NOFS
 		 */
-		if (pflags & PF_MEMALLOC_NORECLAIM)
-			flags &= ~__GFP_DIRECT_RECLAIM;
-		else if (pflags & PF_MEMALLOC_NOIO)
+		if (pflags & PF_MEMALLOC_NOIO)
 			flags &= ~(__GFP_IO | __GFP_FS);
 		else if (pflags & PF_MEMALLOC_NOFS)
 			flags &= ~__GFP_FS;
-- 
2.46.0