Hello all, We are getting processes stuck with /proc/pid/stack listing the following: [<ffffffffac0cd0d2>] io_schedule+0x12/0x40 [<ffffffffac1b4695>] __lock_page+0x105/0x150 [<ffffffffac1b4dc1>] pagecache_get_page+0x161/0x210 [<ffffffffac1d4ab4>] shmem_unused_huge_shrink+0x334/0x3f0 [<ffffffffac251546>] super_cache_scan+0x176/0x180 [<ffffffffac1cb6c5>] shrink_slab+0x275/0x460 [<ffffffffac1d0b8e>] shrink_node+0x10e/0x320 [<ffffffffac1d0f3d>] node_reclaim+0x19d/0x250 [<ffffffffac1be0aa>] get_page_from_freelist+0x16a/0xac0 [<ffffffffac1bed87>] __alloc_pages_nodemask+0x107/0x290 [<ffffffffac06dbc3>] pte_alloc_one+0x13/0x40 [<ffffffffac1ef329>] __pte_alloc+0x19/0x100 [<ffffffffac1f17b8>] alloc_set_pte+0x468/0x4c0 [<ffffffffac1f184a>] finish_fault+0x3a/0x70 [<ffffffffac1f369a>] __handle_mm_fault+0x94a/0x1190 [<ffffffffac1f3fa4>] handle_mm_fault+0xc4/0x1d0 [<ffffffffac0682a3>] __do_page_fault+0x253/0x4d0 [<ffffffffac068553>] do_page_fault+0x33/0x120 [<ffffffffac8019dc>] page_fault+0x4c/0x60 For some reason io_schedule is not coming back, so shrinker_rwsem never gets an up_read. When this happens, other processes like libvirt get stuck trying to start VMs with the /proc/pid/stack of libvirtd looking like so, while register_shrinker waits for shrinker_rwsem to be released: [<ffffffffac7538d3>] call_rwsem_down_write_failed+0x13/0x20 [<ffffffffac1cb985>] register_shrinker+0x45/0xa0 [<ffffffffac250f68>] sget_userns+0x468/0x4a0 [<ffffffffac25106a>] mount_nodev+0x2a/0xa0 [<ffffffffac251be4>] mount_fs+0x34/0x150 [<ffffffffac2701f2>] vfs_kern_mount+0x62/0x120 [<ffffffffac272a0e>] do_mount+0x1ee/0xc50 [<ffffffffac27377e>] SyS_mount+0x7e/0xd0 [<ffffffffac003831>] do_syscall_64+0x61/0x1a0 [<ffffffffac80012c>] entry_SYSCALL64_slow_path+0x25/0x25 [<ffffffffffffffff>] 0xffffffffffffffff I seem to be able to reproduce this somewhat reliably, it will likely be stuck by tomorrow morning. Since it does seem to take a day to hang, I was hoping to avoid a bisect and see if anyone has seen this behavior or knows it to be fixed in 4.15-rc. Note that we are using zram as our only swap device, but at the time that it shrink_slab() failed to return, there was plenty of memory available and no swap was in use. The machine is generally responsive, but `sync` will hang forever and our only way out is `echo b > /proc/sysrq-trigger`. Please suggest any additional information you might need for testing, and I am happy to try patches. Thank you for your help! -- Eric Wheeler -- 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>
