On Tue, Jul 15, 2025 at 11:46:22AM -0700, Keith Busch wrote: > From: Keith Busch <kbusch@xxxxxxxxxx> > > A large DMA mapping request can loop through dma address pinning for > many pages. In cases where THP can not be used, the repeated vmf_insert_pfn can > be costly, so let the task reschedule as need to prevent CPU stalls. Failure to > do so has potential harmful side effects, like increased memory pressure > as unrelated rcu tasks are unable to make their reclaim callbacks and > result in OOM conditions. > > rcu: INFO: rcu_sched self-detected stall on CPU > rcu: 36-....: (20999 ticks this GP) idle=b01c/1/0x4000000000000000 softirq=35839/35839 fqs=3538 > rcu: hardirqs softirqs csw/system > rcu: number: 0 107 0 > rcu: cputime: 50 0 10446 ==> 10556(ms) > rcu: (t=21075 jiffies g=377761 q=204059 ncpus=384) > ... > <TASK> > ? asm_sysvec_apic_timer_interrupt+0x16/0x20 > ? walk_system_ram_range+0x63/0x120 > ? walk_system_ram_range+0x46/0x120 > ? pgprot_writethrough+0x20/0x20 > lookup_memtype+0x67/0xf0 > track_pfn_insert+0x20/0x40 > vmf_insert_pfn_prot+0x88/0x140 > vfio_pci_mmap_huge_fault+0xf9/0x1b0 [vfio_pci_core] > __do_fault+0x28/0x1b0 > handle_mm_fault+0xef1/0x2560 > fixup_user_fault+0xf5/0x270 > vaddr_get_pfns+0x169/0x2f0 [vfio_iommu_type1] > vfio_pin_pages_remote+0x162/0x8e0 [vfio_iommu_type1] > vfio_iommu_type1_ioctl+0x1121/0x1810 [vfio_iommu_type1] > ? futex_wake+0x1c1/0x260 > x64_sys_call+0x234/0x17a0 > do_syscall_64+0x63/0x130 > ? exc_page_fault+0x63/0x130 > entry_SYSCALL_64_after_hwframe+0x4b/0x53 > > Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx> > --- > v1->v2: > > Merged up to vfio/next > > Moved the cond_resched() to a more appropriate place within the > loop, and added a comment about why it's there. > > Update to change log describing one of the consequences of not doing > this. > > drivers/vfio/vfio_iommu_type1.c | 7 +++++++ > 1 file changed, 7 insertions(+) You should be making a matching change to iommufd too.. Jason
