Re: [PATCH v2] mm/memory-failure: fix deadlock when hugetlb_optimize_vmemmap is enabled

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On 4/11/24 7:57 PM, Miaohe Lin wrote:
When I did hard offline test with hugetlb pages, below deadlock occurs:

======================================================
WARNING: possible circular locking dependency detected
6.8.0-11409-gf6cef5f8c37f #1 Not tainted
------------------------------------------------------
bash/46904 is trying to acquire lock:
ffffffffabe68910 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_slow_dec+0x16/0x60

but task is already holding lock:
ffffffffabf92ea8 (pcp_batch_high_lock){+.+.}-{3:3}, at: zone_pcp_disable+0x16/0x40

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (pcp_batch_high_lock){+.+.}-{3:3}:
        __mutex_lock+0x6c/0x770
        page_alloc_cpu_online+0x3c/0x70
        cpuhp_invoke_callback+0x397/0x5f0
        __cpuhp_invoke_callback_range+0x71/0xe0
        _cpu_up+0xeb/0x210
        cpu_up+0x91/0xe0
        cpuhp_bringup_mask+0x49/0xb0
        bringup_nonboot_cpus+0xb7/0xe0
        smp_init+0x25/0xa0
        kernel_init_freeable+0x15f/0x3e0
        kernel_init+0x15/0x1b0
        ret_from_fork+0x2f/0x50
        ret_from_fork_asm+0x1a/0x30

-> #0 (cpu_hotplug_lock){++++}-{0:0}:
        __lock_acquire+0x1298/0x1cd0
        lock_acquire+0xc0/0x2b0
        cpus_read_lock+0x2a/0xc0
        static_key_slow_dec+0x16/0x60
        __hugetlb_vmemmap_restore_folio+0x1b9/0x200
        dissolve_free_huge_page+0x211/0x260
        __page_handle_poison+0x45/0xc0
        memory_failure+0x65e/0xc70
        hard_offline_page_store+0x55/0xa0
        kernfs_fop_write_iter+0x12c/0x1d0
        vfs_write+0x387/0x550
        ksys_write+0x64/0xe0
        do_syscall_64+0xca/0x1e0
        entry_SYSCALL_64_after_hwframe+0x6d/0x75

other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(pcp_batch_high_lock);
                                lock(cpu_hotplug_lock);
                                lock(pcp_batch_high_lock);
   rlock(cpu_hotplug_lock);

  *** DEADLOCK ***

5 locks held by bash/46904:
  #0: ffff98f6c3bb23f0 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x64/0xe0
  #1: ffff98f6c328e488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0xf8/0x1d0
  #2: ffff98ef83b31890 (kn->active#113){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x100/0x1d0
  #3: ffffffffabf9db48 (mf_mutex){+.+.}-{3:3}, at: memory_failure+0x44/0xc70
  #4: ffffffffabf92ea8 (pcp_batch_high_lock){+.+.}-{3:3}, at: zone_pcp_disable+0x16/0x40

stack backtrace:
CPU: 10 PID: 46904 Comm: bash Kdump: loaded Not tainted 6.8.0-11409-gf6cef5f8c37f #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
Call Trace:
  <TASK>
  dump_stack_lvl+0x68/0xa0
  check_noncircular+0x129/0x140
  __lock_acquire+0x1298/0x1cd0
  lock_acquire+0xc0/0x2b0
  cpus_read_lock+0x2a/0xc0
  static_key_slow_dec+0x16/0x60
  __hugetlb_vmemmap_restore_folio+0x1b9/0x200
  dissolve_free_huge_page+0x211/0x260
  __page_handle_poison+0x45/0xc0
  memory_failure+0x65e/0xc70
  hard_offline_page_store+0x55/0xa0
  kernfs_fop_write_iter+0x12c/0x1d0
  vfs_write+0x387/0x550
  ksys_write+0x64/0xe0
  do_syscall_64+0xca/0x1e0
  entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7fc862314887
Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
RSP: 002b:00007fff19311268 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000000000c RCX: 00007fc862314887
RDX: 000000000000000c RSI: 000056405645fe10 RDI: 0000000000000001
RBP: 000056405645fe10 R08: 00007fc8623d1460 R09: 000000007fffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c
R13: 00007fc86241b780 R14: 00007fc862417600 R15: 00007fc862416a00

In short, below scene breaks the lock dependency chain:

  memory_failure
   __page_handle_poison
    zone_pcp_disable -- lock(pcp_batch_high_lock)
    dissolve_free_huge_page
     __hugetlb_vmemmap_restore_folio
      static_key_slow_dec
       cpus_read_lock -- rlock(cpu_hotplug_lock)

Fix this by calling drain_all_pages() instead.

Fixes: a6b40850c442 ("mm: hugetlb: replace hugetlb_free_vmemmap_enabled with a static_key")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Acked-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
v2:
  collect Acked-by tag and extend comment per Oscar. Thanks.
---
  mm/memory-failure.c | 16 +++++++++++++---
  1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index edd6e114462f..c6750509d74c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -153,11 +153,21 @@ static int __page_handle_poison(struct page *page)
  {
  	int ret;
- zone_pcp_disable(page_zone(page));
+	/*
+	 * zone_pcp_disable() can't be used here. It will hold pcp_batch_high_lock and
+	 * dissolve_free_huge_page() might hold cpu_hotplug_lock via static_key_slow_dec()
+	 * when hugetlb vmemmap optimization is enabled. This will break current lock
+	 * dependency chain and leads to deadlock.
+	 * Disabling pcp before dissolving the page was a deterministic approach because
+	 * we made sure that those pages cannot end up in any PCP list. Draining PCP lists
+	 * expels those pages to the buddy system, but nothing guarantees that those pages
+	 * do not get back to a PCP queue if we need to refill those.
+	 */
  	ret = dissolve_free_huge_page(page);

Hi Miaohe,

I recently sent a patch[1] to convert dissolve_free_huge_page() to folios which changes the function name and the name referenced in the comment so this will conflict with my patch. It's in mm-unstable now, would you be able to rebase to that in a new version?

Thanks,
Sid

[1] https://lore.kernel.org/linux-mm/20240411164756.261178-1-sidhartha.kumar@xxxxxxxxxx/T/#u


-	if (!ret)
+	if (!ret) {
+		drain_all_pages(page_zone(page));
  		ret = take_page_off_buddy(page);
-	zone_pcp_enable(page_zone(page));
+	}
return ret;
  }





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