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xfrm: Don't disable preemption while looking up cache state.

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For the state cache lookup xfrm_input_state_lookup() first disables
preemption, to remain on the CPU and then retrieves a per-CPU pointer.
Within the preempt-disable section it also acquires
netns_xfrm::xfrm_state_lock, a spinlock_t. This lock must not be
acquired with explicit disabled preemption (such as by get_cpu())
because this lock becomes a sleeping lock on PREEMPT_RT.

To remain on the same CPU is just an optimisation for the CPU local
lookup. The actual modification of the per-CPU variable happens with
netns_xfrm::xfrm_state_lock acquired.

Remove get_cpu() and use the state_cache_input on the current CPU.

Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Closes: https://lore.kernel.org/all/CAADnVQKkCLaj=roayH=Mjiiqz_svdf1tsC3OE4EC0E=mAD+L1A@mail.gmail.com/
Fixes: 81a331a0e7 ("xfrm: Add an inbound percpu state cache.")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit is contained in:
Sebastian Sewior 2025-01-23 17:20:45 +01:00 committed by Steffen Klassert
parent 1620c88887
commit 6c9b7db96d
1 changed files with 1 additions and 3 deletions
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4
net/xfrm/xfrm_state.c
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@ -1150,9 +1150,8 @@ struct xfrm_state *xfrm_input_state_lookup(struct net *net, u32 mark,
struct xfrm_hash_state_ptrs state_ptrs;
struct hlist_head *state_cache_input;
struct xfrm_state *x = NULL;
int cpu = get_cpu();
state_cache_input = per_cpu_ptr(net->xfrm.state_cache_input, cpu);
state_cache_input = raw_cpu_ptr(net->xfrm.state_cache_input);
rcu_read_lock();
hlist_for_each_entry_rcu(x, state_cache_input, state_cache_input) {
@ -1186,7 +1185,6 @@ struct xfrm_state *xfrm_input_state_lookup(struct net *net, u32 mark,
out:
rcu_read_unlock();
put_cpu();
return x;
}
EXPORT_SYMBOL(xfrm_input_state_lookup);