Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
From: Waiman Long
Date: Mon Nov 21 2022 - 10:13:30 EST
On 11/21/22 05:38, Peter Zijlstra wrote:
On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
set. Unfortunately, some of the callers of do_set_cpus_allowed()
'some' ? There's only 3 or so, which one triggers this?
It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is
called with pi_lock held.
[ 1084.820105] <TASK>
[ 1084.820110] dump_stack_lvl+0x57/0x81
[ 1084.820117] check_noncircular+0x103/0x120
[ 10[ 1084.820160] lock_acquire+0xba/0x230
[ 1084.820164] ? kfree+0x10f/0x380
[ 1084.820172] ? do_set_cpus_allowed+0x40/0x60
[ 1084.820181] rt_spin_lock+0x27/0xe0
[ 1084.820184] ? kfree+0x10f/0x380
[ 1084.820188] kfree+0x10f/0x380
[ 1084.820195] do_set_cpus_allowed+0x40/0x60
[ 1084.820203] kthread_bind_mask+0x4a/0x70
[ 1084.820211] create_worker+0xfb/0x1a0
[ 1084.820220] worker_thread+0x2e3/0x3c0
[ 1084.820226] ? process_one_work+0x450/0x450
[ 1084.820230] kthread+0x111/0x130
[ 1084.820236] ? kthread_complete_and_exit+0x20/0x20
[ 1084.820244] ret_from_fork+0x22/0x30
[ 1084.820258] </TASK>
[ 1084.820260] BUG: sleeping function called from invalid context at
kernel/locking/spinlock_rt.c:46
It shows up with PREEMPT_RT kernel.
may not be in a context where kfree() can be safely called. So the
following splats may be printed:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context
To avoid these problems without leaking memory, the free cpumask is now
put into a lockless list to be reused in a later sched_setaffinity()
call instead.
Urgh.. depending on which of the callsites it is, it's probably simpler
to just rework the caller to not use do_set_cpus_allowed(), no?
Maybe. One thing that I am not clear about is why user_cpus_ptr is set
in the first place.
Cheers,
Longman