On 8/28/25 3:28 AM, Li Nan wrote: > > > ? 2025/8/27 16:10, Ming Lei ??: >> On Wed, Aug 27, 2025 at 11:22:06AM +0800, Li Nan wrote: >>> >>> >>> ? 2025/8/27 9:35, Ming Lei ??: >>>> On Wed, Aug 27, 2025 at 09:04:45AM +0800, Yu Kuai wrote: >>>>> Hi, >>>>> >>>>> ? 2025/08/27 8:58, Ming Lei ??: >>>>>> On Tue, Aug 26, 2025 at 04:48:54PM +0800, linan666@xxxxxxxxxxxxxxx wrote: >>>>>>> From: Li Nan <linan122@xxxxxxxxxx> >>>>>>> >>>>>>> In __blk_mq_update_nr_hw_queues() the return value of >>>>>>> blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx >>>>>> >>>>>> Looks we should check its return value and handle the failure in both >>>>>> the call site and blk_mq_sysfs_register_hctxs(). >>>>> >>>>> From __blk_mq_update_nr_hw_queues(), the old hctxs is already >>>>> unregistered, and this function is void, we failed to register new hctxs >>>>> because of memory allocation failure. I really don't know how to handle >>>>> the failure here, do you have any suggestions? >>>> >>>> It is out of memory, I think it is fine to do whatever to leave queue state >>>> intact instead of making it `partial workable`, such as: >>>> >>>> - try update nr_hw_queues to 1 >>>> >>>> - if it still fails, delete disk & mark queue as dead if disk is attached >>>> >>> >>> If we ignore these non-critical sysfs creation failures, the disk remains >>> usable with no loss of functionality. Deleting the disk seems to escalate >>> the error? >> >> It is more like a workaround by ignoring the sysfs register failure. And if >> the issue need to be fixed in this way, you have to document it. > >> In case of OOM, it usually means that the system isn't usable any more. >> But it is NOIO allocation and the typical use case is for error recovery in >> nvme pci, so there may not be enough pages for noio allocation only. That is >> the reason for ignoring sysfs register in blk_mq_update_nr_hw_queues()? >> >> But NVMe has been pretty fragile in this area by using non-owner queue >> freeze, and call blk_mq_update_nr_hw_queues() on frozen queue, so it is >> really necessary to take it into account? > > I agree with your points about NOIO and NVMe. > > I hit this issue in null_blk during fuzz testing with memory-fault > injection. Changing the number of hardware queues under OOM is > extremely rare in real-world usage. So I think adding a workaround and > documenting it is sufficient. What do you think? Working around it is fine, as it isn't a situation we really need to worry about. But let's please not do it by poking at kobject internals. -- Jens Axboe
