Michal Hocko wrote: > On Wed 15-11-17 09:00:20, Johannes Weiner wrote: > > In any case, Minchan's lock breaking seems way preferable over that > > level of headscratching complexity for an unusual case like Shakeel's. > > agreed! I would go the more complex way only if it turns out that early > break out causes some real problems. > Eric Wheeler wrote (at http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@xxxxxxxxxxxxxxxxx ): > Hello all, > > We are getting processes stuck with /proc/pid/stack listing the following: Yes, I think that this is a silent OOM lockup. > > [<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 > If io_schedule() depends on somebody else's memory allocation request, that somebody else will call shrink_slab() and down_read_trylock(&shrinker_rwsem) will fail without making progress. This means that that somebody else will forever retry as long as should_continue_reclaim() returns true. I don't know what is causing should_continue_reclaim() to return true, but nobody will be able to reclaim memory because down_read_trylock(&shrinker_rwsem) continues failing without making progress. > > 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. I think that this problem is not yet fixed in linux-next.git . > > 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! Pretending we will be able to make progress if (!down_read_trylock(&shrinker_rwsem)) { /* * If we would return 0, our callers would understand that we * have nothing else to shrink and give up trying. By returning * 1 we keep it going and assume we'll be able to shrink next * time. */ freed = 1; goto out; } can work only if do_shrink_slab() does not depend on somebody else's memory allocation. I think we should kill shrinker_rwsem assumption. -- 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>
