Re: [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack

[Qian Cai]

On Fri, Jun 05, 2020 at 07:36:22PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 05, 2020 at 01:18:16PM -0400, Qian Cai wrote:
> > On Thu, May 21, 2020 at 10:05:23PM +0200, Thomas Gleixner wrote:
> > > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > 
> > > Device interrupt handlers and system vector handlers are executed on the
> > > interrupt stack. The stack switch happens in the low level assembly entry
> > > code. This conflicts with the efforts to consolidate the exit code in C to
> > > ensure correctness vs. RCU and tracing.
> > > 
> > > As there is no way to move #DB away from IST due to the MOV SS issue, the
> > > requirements vs. #DB and NMI for switching to the interrupt stack do not
> > > exist anymore. The only requirement is that interrupts are disabled.
> > > 
> > > That allows to move the stack switching to C code which simplifies the
> > > entry/exit handling further because it allows to switch stacks after
> > > handling the entry and on exit before handling RCU, return to usermode and
> > > kernel preemption in the same way as for regular exceptions.
> > > 
> > > The initial attempt of having the stack switching in inline ASM caused too
> > > much headache vs. objtool and the unwinder. After analysing the use cases
> > > it was agreed on that having the stack switch in ASM for the price of an
> > > indirect call is acceptable as the main users are indirect call heavy
> > > anyway and the few system vectors which are empty shells (scheduler IPI and
> > > KVM posted interrupt vectors) can run from the regular stack.
> > > 
> > > Provide helper functions to check whether the interrupt stack is already
> > > active and whether stack switching is required.
> > > 
> > > 64 bit only for now. 32 bit has a variant of that already. Once this is
> > > cleaned up the two implementations might be consolidated as a cleanup on
> > > top.
> > > 
> > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > 
> > Reverted this commit and the rest of series (with trivial fixup) as well
> > as the two dependencies [1],
> > 
> > 8449e768dcb8 ("x86/entry: Remove debug IDT frobbing")
> > 029149180d1d ("x86/entry: Rename trace_hardirqs_off_prepare()")
> > 
> > fixed the warning under some memory pressure on AMD NUMA servers.
> 
> The warning ?

Obviously, the warning below.

> 
> > [ 9371.959858]  asm_call_on_stack+0x12/0x20
> > asm_call_on_stack at arch/x86/entry/entry_64.S:710

This is one piece of call from the warning call traces that introduced
by the patch which leads me to revert the commit in the first place. It
may or may not be the real culprit, but just wanted to highlight it in
case. 

> 
> ^^ what's that?
> 
> > The .config (if ever matters),
> > https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
> > 
> > [ 9371.260161] ------------[ cut here ]------------
> > [ 9371.267143] Stack depot reached limit capacity
> > [ 9371.267193] WARNING: CPU: 19 PID: 1181 at lib/stackdepot.c:115 stack_depot_save+0x3d9/0x57d
> 
> Is this _the_ warning?
> 
> Maybe it really is running out of storage, I don't think this patch is
> to blame. The unwind here looks good, so why would the stack-depot
> unwind be any different?

Don't know. It is always reproducible with the same warning and call
traces on multiple similar AMD servers. Can this patch (or series)
increase the storage so much or some kind of recursion? Otherwise, never
saw this problem before the series was introduced. It is always running
almost the same tests for years on those machines.

> 
> > [ 9371.281470] Modules linked in: brd vfat fat ext4 crc16 mbcache jbd2 loop kvm_amd kvm ses enclosure dax_pmem irqbypass dax_pmem_core acpi_cpufreq ip_tables x_table
> > s xfs sd_mod bnxt_en smartpqi scsi_transport_sas tg3 i40e libphy firmware_class dm_mirror dm_region_hash dm_log dm_mod [last unloaded: dummy_del_mod]
> > [ 9371.310176] CPU: 19 PID: 1181 Comm: systemd-journal Tainted: G           O      5.7.0-next-20200604+ #1
> > [ 9371.320700] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 03/09/2018
> > [ 9371.329987] RIP: 0010:stack_depot_save+0x3d9/0x57d
> > [ 9371.335513] Code: 1d 9b bc 68 01 80 fb 01 0f 87 c0 01 00 00 80 e3 01 75 1f 4c 89 45 c0 c6 05 82 bc 68 01 01 48 c7 c7 e0 85 63 9f e8 9d 74 9d ff <0f> 0b 90 90 4c 8
> > b 45 c0 48 c7 c7 80 1a d0 9f 4c 89 c6 e8 b0 2b 46
> > [ 9371.355426] RSP: 0018:ffffc90007260490 EFLAGS: 00010082
> > [ 9371.361387] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff9ed3207f
> > [ 9371.369544] RDX: 0000000000000007 RSI: dffffc0000000000 RDI: 0000000000000000
> > [ 9371.377428] RBP: ffffc900072604f8 R08: fffffbfff3f37539 R09: fffffbfff3f37539
> > [ 9371.385310] R10: ffffffff9f9ba9c3 R11: fffffbfff3f37538 R12: ffffc90007260508
> > [ 9371.393521] R13: 0000000000000036 R14: 0000000000000000 R15: 000000000009fb52
> > [ 9371.401403] FS:  00007fc9849f2980(0000) GS:ffff88942fb80000(0000) knlGS:0000000000000000
> > [ 9371.410244] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 9371.417007] CR2: 00007f20d02c3000 CR3: 0000000440b9c000 CR4: 00000000003406e0
> > [ 9371.424889] Call Trace:
> > [ 9371.428054]  <IRQ>
> > [ 9371.436315]  save_stack+0x3f/0x50
> > [ 9371.734034]  kasan_slab_free+0xe/0x10
> > [ 9371.738798]  slab_free_freelist_hook+0x5d/0x1c0
> > [ 9371.748886]  kmem_cache_free+0x10c/0x390
> > [ 9371.758450]  mempool_free_slab+0x17/0x20
> > [ 9371.763522]  mempool_free+0x65/0x170
> > [ 9371.767825]  bio_free+0x14c/0x210
> > [ 9371.771864]  bio_put+0x59/0x70
> > [ 9371.775644]  end_swap_bio_write+0x199/0x250
> > [ 9371.780556]  bio_endio+0x22c/0x4e0
> > [ 9371.784709]  dec_pending+0x1bf/0x3e0 [dm_mod]
> > [ 9371.790207]  clone_endio+0x129/0x3d0 [dm_mod]
> > [ 9371.800746]  bio_endio+0x22c/0x4e0
> > [ 9371.809262]  blk_update_request+0x3bb/0x980
> > [ 9371.814605]  scsi_end_request+0x53/0x420
> > [ 9371.824002]  scsi_io_completion+0x10a/0x830
> > [ 9371.844445]  scsi_finish_command+0x1b9/0x250
> > [ 9371.849445]  scsi_softirq_done+0x1ab/0x1f0
> > [ 9371.854272]  blk_mq_force_complete_rq+0x217/0x250
> > [ 9371.859708]  blk_mq_complete_request+0xe/0x20
> > [ 9371.865171]  scsi_mq_done+0xc1/0x220
> > [ 9371.869479]  pqi_aio_io_complete+0x83/0x2c0 [smartpqi]
> > [ 9371.881764]  pqi_irq_handler+0x1fc/0x13f0 [smartpqi]
> > [ 9371.914115]  __handle_irq_event_percpu+0x81/0x550
> > [ 9371.924289]  handle_irq_event_percpu+0x70/0x100
> > [ 9371.945559]  handle_irq_event+0x5a/0x8b
> > [ 9371.950121]  handle_edge_irq+0x10c/0x370
> > [ 9371.950121]  handle_edge_irq+0x10c/0x370
> > [ 9371.959858]  asm_call_on_stack+0x12/0x20
> > asm_call_on_stack at arch/x86/entry/entry_64.S:710
> > [ 9371.964899]  </IRQ>
> > [ 9371.967716]  common_interrupt+0x185/0x2a0
> > [ 9371.972455]  asm_common_interrupt+0x1e/0x40
> > [ 9371.977368] RIP: 0010:__asan_load4+0x8/0xa0
> > [ 9371.982281] Code: 00 e8 5c f4 ff ff 5d c3 40 38 f0 0f 9e c0 84 c0 75 e5 5d c3 48 c1 e8 03 80 3c 10 00 75 ed 5d c3 66 90 55 48 89 e5 48 8b 4d 08 <48> 83 ff fb 77 6c eb 3a 0f 1f 00 48 b8 00 00 00 00 00 00 00 ff 48
> > [ 9372.002246] RSP: 0018:ffffc9000b12f0e8 EFLAGS: 00000202
> > [ 9372.008207] RAX: 0000000000000000 RBX: ffffc9000b12f150 RCX: ffffffff9ed32487
> > [ 9372.016489] RDX: 0000000000000007 RSI: 0000000000000002 RDI: ffffffff9ff92a94
> > [ 9372.024370] RBP: ffffc9000b12f0e8 R08: fffffbfff3ff1d4d R09: fffffbfff3ff1d4d
> > [ 9372.032252] R10: ffffffff9ff8ea67 R11: fffffbfff3ff1d4c R12: 0000000000000000
> > [ 9372.040490] R13: ffffc9000b12f358 R14: 000000000000000c R15: 0000000000000005
> > [ 9372.053899]  debug_lockdep_rcu_enabled+0x27/0x60
> > [ 9372.059248]  rcu_read_lock_held_common+0x12/0x60
> > [ 9372.064989]  rcu_read_lock_sched_held+0x60/0xe0
> > [ 9372.080338]  shrink_active_list+0xbfd/0xc30
> > [ 9372.120481]  shrink_lruvec+0xbf1/0x11b0
> > [ 9372.150410]  shrink_node+0x344/0xd10
> > [ 9372.154719]  do_try_to_free_pages+0x263/0xa00
> > [ 9372.169860]  try_to_free_pages+0x239/0x570
> > [ 9372.179356]  __alloc_pages_slowpath.constprop.59+0x5dd/0x1880
> > [ 9372.215762]  __alloc_pages_nodemask+0x562/0x670
> > [ 9372.232686]  alloc_pages_current+0x9c/0x110
> > [ 9372.237599]  alloc_slab_page+0x355/0x530
> > [ 9372.242755]  allocate_slab+0x485/0x5a0
> > [ 9372.247232]  new_slab+0x46/0x70
> > [ 9372.251095]  ___slab_alloc+0x35f/0x810
> > [ 9372.274485]  __slab_alloc+0x43/0x70
> > [ 9372.287650]  kmem_cache_alloc+0x257/0x3d0
> > [ 9372.298182]  prepare_creds+0x26/0x130
> > [ 9372.302571]  do_faccessat+0x255/0x3e0
> > [ 9372.321591]  __x64_sys_access+0x38/0x40
> > [ 9372.326154]  do_syscall_64+0x64/0x340
> > [ 9372.330542]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 9372.336329] RIP: 0033:0x7fc983a21bfb
> > [ 9372.341050] Code: Bad RIP value.
> > [ 9372.345000] RSP: 002b:00007fffd543cde8 EFLAGS: 00000246 ORIG_RAX: 0000000000000015
> > [ 9372.353319] RAX: ffffffffffffffda RBX: 00007fffd543fa40 RCX: 00007fc983a21bfb
> > [ 9372.361199] RDX: 00007fc983cf1c00 RSI: 0000000000000000 RDI: 00005573ed458090
> > [ 9372.369512] RBP: 00007fffd543cf30 R08: 00005573ed44ab99 R09: 0000000000000007
> > [ 9372.377393] R10: 0000000000000041 R11: 0000000000000246 R12: 0000000000000000
> > [ 9372.385275] R13: 0000000000000000 R14: 00007fffd543cea0 R15: 00005573eecd2990
> > [ 9372.393608] irq event stamp: 27274496
> > [ 9372.397999] hardirqs last  enabled at (27274495): [<ffffffff9e635b8e>] free_unref_page_list+0x2ee/0x400
> > [ 9372.408152] hardirqs last disabled at (27274496): [<ffffffff9ed2c22b>] idtentry_enter_cond_rcu+0x1b/0x50
> > [ 9372.418695] softirqs last  enabled at (27272816): [<ffffffff9f000478>] __do_softirq+0x478/0x784
> > [ 9372.428154] softirqs last disabled at (27272807): [<ffffffff9e2d0b41>] irq_exit_rcu+0xd1/0xe0
> > [ 9372.437435] ---[ end trace d2ebac1fad6e452e ]---