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a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=6UeiqGixMTsA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=HfqzDRm77vvMm0GhDc0A:9 a=CjuIK1q_8ugA:10 cc=ntf awl=host:12096 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTA5MDE4MCBTYWx0ZWRfX3tmEXbPtFX6s YNo4DCp1QqALZmFGRyMQRQ2HoMDwS4mBfxiNfspCG1xX5MzylZ6RfNJPH+xmLv/hhK1MwWT/Kb0 9Zvlp+/8t9U2zc5Gh2fBQAt+CiL8AzkGbyfctUSqbX0DY2iiOZ7TQ1kbTHjQ/4qGQF3FPhJFstj U2Cy8PQhTlf9Wi0n9G2e9ZBUTQldFLVuYz1Tv3VVcL6Yikz8krRqkb6Py2nff+RiDGeShzULinO ZDyMy7kfx6/ypbf9TL4u4uwJZ+teKFD3k9K6U9o6Y9VhWrDs0A4f4XGnnNdV86e19mtvHQ0Pkrw QthLeVfzMdvjn136E3Jz1NCO+t3gsbC8WheqbpwX3sA2I35JsrbhY7wTXeB9NJgxIcARUG8Fj12 qNz33pM/iFP83AiJcaIzb5SSTYyqOFhjqLSrptKfdKpbdBJDY+4= On Fri, Nov 07, 2025 at 10:32:52PM -0800, Shakeel Butt wrote: > On Fri, Nov 07, 2025 at 10:20:57PM +0900, Harry Yoo wrote: > > > > Although it's mentioned in the locking documentation, I'm afraid that > > local_lock is not the right interface to use here. Preemption will be > > disabled anyway (on both PREEMPT_RT and !PREEMPT_RT) when the stats are > > updated (in __mod_node_page_state()). > > > > Here we just want to disable IRQ only on !PREEMPT_RT (to update > > the stats safely). > > I don't think there is a need to disable IRQs. There are three stats > update functions called in that hunk. > > 1) __mod_lruvec_state > 2) __count_vm_events > 3) count_memcg_events > > count_memcg_events() can be called with IRQs. __count_vm_events can be > replaced with count_vm_events. Right. > For __mod_lruvec_state, the > __mod_node_page_state() inside needs preemption disabled. The function __mod_node_page_state() disables preemption. And there's a comment in __mod_zone_page_state(): > /* > * Accurate vmstat updates require a RMW. On !PREEMPT_RT kernels, > * atomicity is provided by IRQs being disabled -- either explicitly > * or via local_lock_irq. On PREEMPT_RT, local_lock_irq only disables > * CPU migrations and preemption potentially corrupts a counter so > * disable preemption. > */ > preempt_disable_nested(); We're relying on IRQs being disabled on !PREEMPT_RT. Maybe we could make it safe against re-entrant IRQ handlers by using read-modify-write operations? -- Cheers, Harry / Hyeonggon > Easy way would be to just disable/enable preemption instead of IRQs. > Otherwise go a bit more fine-grained approach i.e. replace > __count_vm_events with count_vm_events and just disable preemption > across __mod_node_page_state().