Messages in this thread | | | Date | Mon, 21 Nov 2022 10:04:33 -0500 | Subject | Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed() | From | Waiman Long <> |
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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
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