From: Adrian Huang ahuang12@lenovo.com Subject: mm: memcg/slab: call flush_memcg_workqueue() only if memcg workqueue is valid

When booting with amd_iommu=off, the following WARNING message appears: AMD-Vi: AMD IOMMU disabled on kernel command-line ------------[ cut here ]------------ WARNING: CPU: 0 PID: 0 at kernel/workqueue.c:2772 flush_workqueue+0x42e/0x450 Modules linked in: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.5.0-rc3-amd-iommu #6 Hardware name: Lenovo ThinkSystem SR655-2S/7D2WRCZ000, BIOS D8E101L-1.00 12/05/2019 RIP: 0010:flush_workqueue+0x42e/0x450 Code: ff 0f 0b e9 7a fd ff ff 4d 89 ef e9 33 fe ff ff 0f 0b e9 7f fd ff ff 0f 0b e9 bc fd ff ff 0f 0b e9 a8 fd ff ff e8 52 2c fe ff <0f> 0b 31 d2 48 c7 c6 e0 88 c5 95 48 c7 c7 d8 ad f0 95 e8 19 f5 04 RSP: 0000:ffffffff96203d80 EFLAGS: 00010246 RAX: ffffffff96203dc8 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffffffff96a63120 RSI: ffffffff95efcba2 RDI: ffffffff96203dc0 RBP: ffffffff96203e08 R08: 0000000000000000 R09: ffffffff962a1828 R10: 00000000f0000080 R11: dead000000000100 R12: ffff8d8a87c0a770 R13: dead000000000100 R14: 0000000000000456 R15: ffffffff96203da0 FS: 0000000000000000(0000) GS:ffff8d8dbd000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff8d91cfbff000 CR3: 000000078920a000 CR4: 00000000000406b0 Call Trace: ? wait_for_completion+0x51/0x180 kmem_cache_destroy+0x69/0x260 iommu_go_to_state+0x40c/0x5ab amd_iommu_prepare+0x16/0x2a irq_remapping_prepare+0x36/0x5f enable_IR_x2apic+0x21/0x172 default_setup_apic_routing+0x12/0x6f apic_intr_mode_init+0x1a1/0x1f1 x86_late_time_init+0x17/0x1c start_kernel+0x480/0x53f secondary_startup_64+0xb6/0xc0 ---[ end trace 30894107c3749449 ]--- x2apic: IRQ remapping doesn't support X2APIC mode x2apic disabled

The warning is caused by the calling of 'kmem_cache_destroy()' in free_iommu_resources(). Here is the call path: free_iommu_resources kmem_cache_destroy flush_memcg_workqueue flush_workqueue

The root cause is that the IOMMU subsystem runs before the workqueue subsystem, which the variable 'wq_online' is still 'false'. This leads to the statement 'if (WARN_ON(!wq_online))' in flush_workqueue() is 'true'.

Since the variable 'memcg_kmem_cache_wq' is not allocated during the time, it is unnecessary to call flush_memcg_workqueue(). This prevents the WARNING message triggered by flush_workqueue().

Link: http://lkml.kernel.org/r/20200103085503.1665-1-ahuang12@lenovo.com Fixes: 92ee383f6daab ("mm: fix race between kmem_cache destroy, create and deactivate") Signed-off-by: Adrian Huang ahuang12@lenovo.com Reported-by: Xiaochun Lee lixc17@lenovo.com Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Joerg Roedel jroedel@suse.de Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Michal Hocko mhocko@kernel.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/slab_common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/slab_common.c~mm-memcg-slab-call-flush_memcg_workqueue-only-if-memcg-workqueue-is-valid +++ a/mm/slab_common.c @@ -903,7 +903,8 @@ static void flush_memcg_workqueue(struct * deactivates the memcg kmem_caches through workqueue. Make sure all * previous workitems on workqueue are processed. */ - flush_workqueue(memcg_kmem_cache_wq); + if (likely(memcg_kmem_cache_wq)) + flush_workqueue(memcg_kmem_cache_wq);

/* * If we're racing with children kmem_cache deactivation, it might _