Messages in this thread | | | Subject | Re: [PATCH] xen/events: events_fifo: Don't use {get,put}_cpu() in xen_evtchn_fifo_init() | From | Julien Grall <> | Date | Tue, 22 Aug 2017 17:15:24 +0100 |
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Hi,
Gentle ping. This patch was reviewed but not queued. Are we waiting for other reviewed?
Cheers,
On 18/08/17 11:15, Julien Grall wrote: > Hi Boris, > > On 17/08/17 18:36, Boris Ostrovsky wrote: >> On 08/17/2017 12:14 PM, Julien Grall wrote: >>> When booting Linux as Xen guest with CONFIG_DEBUG_ATOMIC, the following >>> splat appears: >>> >>> [ 0.002323] Mountpoint-cache hash table entries: 1024 (order: 1, >>> 8192 bytes) >>> [ 0.019717] ASID allocator initialised with 65536 entries >>> [ 0.020019] xen:grant_table: Grant tables using version 1 layout >>> [ 0.020051] Grant table initialized >>> [ 0.020069] BUG: sleeping function called from invalid context at >>> /data/src/linux/mm/page_alloc.c:4046 >>> [ 0.020100] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: >>> swapper/0 >>> [ 0.020123] no locks held by swapper/0/1. >>> [ 0.020143] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc5 #598 >>> [ 0.020166] Hardware name: FVP Base (DT) >>> [ 0.020182] Call trace: >>> [ 0.020199] [<ffff00000808a5c0>] dump_backtrace+0x0/0x270 >>> [ 0.020222] [<ffff00000808a95c>] show_stack+0x24/0x30 >>> [ 0.020244] [<ffff000008c1ef20>] dump_stack+0xb8/0xf0 >>> [ 0.020267] [<ffff0000081128c0>] ___might_sleep+0x1c8/0x1f8 >>> [ 0.020291] [<ffff000008112948>] __might_sleep+0x58/0x90 >>> [ 0.020313] [<ffff0000082171b8>] __alloc_pages_nodemask+0x1c0/0x12e8 >>> [ 0.020338] [<ffff00000827a110>] alloc_page_interleave+0x38/0x88 >>> [ 0.020363] [<ffff00000827a904>] alloc_pages_current+0xdc/0xf0 >>> [ 0.020387] [<ffff000008211f38>] __get_free_pages+0x28/0x50 >>> [ 0.020411] [<ffff0000086566a4>] >>> evtchn_fifo_alloc_control_block+0x2c/0xa0 >>> [ 0.020437] [<ffff0000091747b0>] xen_evtchn_fifo_init+0x38/0xb4 >>> [ 0.020461] [<ffff0000091746c0>] xen_init_IRQ+0x44/0xc8 >>> [ 0.020484] [<ffff000009128adc>] xen_guest_init+0x250/0x300 >>> [ 0.020507] [<ffff000008083974>] do_one_initcall+0x44/0x130 >>> [ 0.020531] [<ffff000009120df8>] kernel_init_freeable+0x120/0x288 >>> [ 0.020556] [<ffff000008c31ca8>] kernel_init+0x18/0x110 >>> [ 0.020578] [<ffff000008083710>] ret_from_fork+0x10/0x40 >>> [ 0.020606] xen:events: Using FIFO-based ABI >>> [ 0.020658] Xen: initializing cpu0 >>> [ 0.027727] Hierarchical SRCU implementation. >>> [ 0.036235] EFI services will not be available. >>> [ 0.043810] smp: Bringing up secondary CPUs ... >>> >>> This is because get_cpu() in xen_evtchn_fifo_init() will disable >>> preemption, but __get_free_page() might sleep (GFP_ATOMIC is not set). >>> >>> xen_evtchn_fifo_init() will always be called before SMP is initialized, >>> so {get,put}_cpu() could be replaced by a simple smp_processor_id(). >> >> On x86 this will be called out of init_IRQ(), which is already preceded >> by preempt_disable(). > > Well the main problem is preempt_disable() itself. in_atomic() will > check preempt_count and return 1 if it is non-zero. > > __get_free_page might sleep if GFP_ATOMIC is not set and therefore you > will see the splat when CONFIG_DEBUG_ATOMIC is enabled. However, those > checks don't happen before the scheduler is setup. Hence why you don't > see the error on x86. > > Cheers, > >> >> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> >> >
-- Julien Grall
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