Hi Hugh, On Mon, Jun 30, 2014 at 04:55:10PM -0700, Hugh Dickins wrote: > Hi Hannes, > > Your rewrite of the memcg charge/uncharge API is bold and attractive, > but I'm having some problems with the way release_pages() now does > uncharging in I/O completion context. Yes, I need to make the uncharge path IRQ-safe. This looks doable. > At the bottom see the lockdep message I get when I start shmem swapping. > Which I have not begun to attempt to decipher (over to you!), but I do > see release_pages() mentioned in there (also i915, hope it's irrelevant). This seems to be about uncharge acquiring the IRQ-unsafe soft limit tree lock while the outer release_pages() holds the IRQ-safe lru_lock. A separate issue, AFAICS, that would also be fixed by IRQ-proofing the uncharge path. > Which was already worrying me on the PowerPC G5, when moving tasks from > one memcg to another and removing the old, while swapping and swappingoff > (I haven't tried much else actually, maybe it's much easier to reproduce). > > I get "unable to handle kernel paging at 0x180" oops in __raw_spinlock < > res_counter_uncharge_until < mem_cgroup_uncharge_end < release_pages < > free_pages_and_swap_cache < tlb_flush_mmu_free < tlb_finish_mmu < > unmap_region < do_munmap (or from exit_mmap < mmput < do_exit). > > I do have CONFIG_MEMCG_SWAP=y, and I think 0x180 corresponds to the > memsw res_counter spinlock, if memcg is NULL. I don't understand why > usually the PowerPC: I did see something like it once on this x86 laptop, > maybe having lockdep in on this slows things down enough not to hit that. > > I've stopped those crashes with patch below: the memcg_batch uncharging > was never designed for use from interrupts. But I bet it needs more work: > to disable interrupts, or do something clever with atomics, or... over to > you again. I was convinced I had tested these changes with lockdep enabled, but it must have been at an earlier stage while developing the series. Otherwise, I should have gotten the same splat as you report. Thanks for the report, I hope to have something useful ASAP. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>