On Thu, Jun 24, 2021 at 02:21:21PM +0200, Michal Hocko wrote: > On Tue 22-06-21 18:50:30, Rafael Aquini wrote: > > On non-preemptible kernel builds the watchdog can complain > > about soft lockups when vfree() is called against large > > vmalloc areas: > > > > [ 210.851798] kvmalloc-test: vmalloc(2199023255552) succeeded > > [ 238.654842] watchdog: BUG: soft lockup - CPU#181 stuck for 26s! [rmmod:5203] > > [ 238.662716] Modules linked in: kvmalloc_test(OE-) ... > > [ 238.772671] CPU: 181 PID: 5203 Comm: rmmod Tainted: G S OE 5.13.0-rc7+ #1 > > [ 238.781413] Hardware name: Intel Corporation PURLEY/PURLEY, BIOS PLYXCRB1.86B.0553.D01.1809190614 09/19/2018 > > [ 238.792383] RIP: 0010:free_unref_page+0x52/0x60 > > [ 238.797447] Code: 48 c1 fd 06 48 89 ee e8 9c d0 ff ff 84 c0 74 19 9c 41 5c fa 48 89 ee 48 89 df e8 b9 ea ff ff 41 f7 c4 00 02 00 00 74 01 fb 5b <5d> 41 5c c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 f0 29 77 > > [ 238.818406] RSP: 0018:ffffb4d87868fe98 EFLAGS: 00000206 > > [ 238.824236] RAX: 0000000000000000 RBX: 000000001da0c945 RCX: ffffb4d87868fe40 > > [ 238.832200] RDX: ffffd79d3beed108 RSI: ffffd7998501dc08 RDI: ffff9c6fbffd7010 > > [ 238.840166] RBP: 000000000d518cbd R08: ffffd7998501dc08 R09: 0000000000000001 > > [ 238.848131] R10: 0000000000000000 R11: ffffd79d3beee088 R12: 0000000000000202 > > [ 238.856095] R13: ffff9e5be3eceec0 R14: 0000000000000000 R15: 0000000000000000 > > [ 238.864059] FS: 00007fe082c2d740(0000) GS:ffff9f4c69b40000(0000) knlGS:0000000000000000 > > [ 238.873089] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 238.879503] CR2: 000055a000611128 CR3: 000000f6094f6006 CR4: 00000000007706e0 > > [ 238.887467] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > [ 238.895433] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > [ 238.903397] PKRU: 55555554 > > [ 238.906417] Call Trace: > > [ 238.909149] __vunmap+0x17c/0x220 > > [ 238.912851] __x64_sys_delete_module+0x13a/0x250 > > [ 238.918008] ? syscall_trace_enter.isra.20+0x13c/0x1b0 > > [ 238.923746] do_syscall_64+0x39/0x80 > > [ 238.927740] entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > Like in other range zapping routines that iterate over > > a large list, lets just add cond_resched() within __vunmap()'s > > page-releasing loop in order to avoid the watchdog splats. > > cond_resched makes a lot of sense. We do not want vmalloc to be visible > the userspace (e.g. by stalling it) so all time consuming operations > should yield regularly whenever possible. I would expect that any > susbsystem which needs huge vmalloc areas would have it for the whole > boot life time so such large vfrees should be really rare. > There is at least one more place with potentially similar issue. I see that the bulk allocator disables irqs during obtaining pages and filling an array. So i suspect if we request a huge size to allocate over vmalloc same soft lockup should occur. For example 10G alloactions simultaneously on different CPUs. I will try to reproduce it on !CONFIG_PREEMPT kernel and post feedback here. -- Vlad Rezki
