mm/slab: disallow kfree_rcu_sheaf() on PREEMPT_RT again

Browse source

This partially reverts commit 2a8bb29ec9 ("mm/slab: allow
kfree_rcu_sheaf() on PREEMPT_RT"). It was based on the assumption that
local_trylock() is safe on PREEMPT_RT from any context.

However kvfree_rcu() is also called by set_cpus_allowed_force() with
task_struct::pi_lock acquired and there it's not safe, as syzbot
has reported.

For the immediate fix, skip kfree_rcu_sheaf() on PREEMPT_RT again from
kvfree_call_rcu(). In theory, kfree_rcu_nolock() would have the same
problem when called from under pi_lock on PREEMPT_RT but that can
be addressed if such a caller is proposed.

Add an explanation comment, courtesy of Sebastian.

Reported-by: syzbot+acf142088e0182172e58@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=acf142088e0182172e58
Reported-by: ThangNN99 <ngocthang2710.1999@gmail.com>
Fixes: 2a8bb29ec9 ("mm/slab: allow kfree_rcu_sheaf() on PREEMPT_RT")
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20260831-b4-kfree_rcu_hotfix-v1-1-4f0fb882638b@kernel.org
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

...

This commit is contained in:

Vlastimil Babka (SUSE) 2026-08-31 18:02:38 +02:00

parent cee9395acd

commit 5541d89758

2 changed files with 11 additions and 12 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

18

mm/slab_common.c

View file

5

mm/slub.c

View file