linux-kernel - [PATCH v3 0/3] cheaper MAY_EXEC handling for path lookup

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Message-ID: <20251107142149.989998-1-mjguzik@gmail.com>
Date: Fri,  7 Nov 2025 15:21:46 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org,
	tytso@....edu,
	torvalds@...ux-foundation.org,
	josef@...icpanda.com,
	linux-btrfs@...r.kernel.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH v3 0/3] cheaper MAY_EXEC handling for path lookup

Commit message in patch 1 says it all.

In short, MAY_WRITE checks are elided.

This obsoletes the idea of pre-computing if perm checks are necessary as
that turned out to be too hairy. The new code has 2 more branches per
path component compared to that idea, but the perf difference for
typical paths (< 6 components) was basically within noise. To be
revisited if someone(tm) removes other slowdowns.

Instead of the pre-computing thing I added IOP_FASTPERM_MAY_EXEC so that
filesystems like btrfs can still avoid the hard work.

v3:
- drop the pre-computation idea and inline the perm check
- add IOP_FASTPERM_MAY_EXEC for filesystems with ->permission hooks so
  that they can also take advantage of it

Mateusz Guzik (3):
  fs: speed up path lookup with cheaper handling of MAY_EXEC
  btrfs: utilize IOP_FASTPERM_MAY_EXEC
  fs: retire now stale MAY_WRITE predicts in inode_permission()

 fs/btrfs/inode.c   | 12 +++++++++++-
 fs/namei.c         | 47 ++++++++++++++++++++++++++++++++++++++++++----
 include/linux/fs.h | 13 +++++++------
 3 files changed, 61 insertions(+), 11 deletions(-)

-- 
2.48.1