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SubjectRe: [PATCH] arch/sh: use slow path for get_user_pages_fast() on SMP
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Hello!

On 06/15/2018 06:52 PM, Thomas Petazzoni wrote:

> The fast path of get_user_pages_fast() disables IRQs and then does:
>
> - gup_pud_range()
> - gup_pmd_range()
> - gup_pte_range()
> - flush_dcache_page()
>
> However, flush_dcache_page() makes a smp_call_function(), and using
> smp_call_function() when IRQs are disabled is not allowed.
>
> In order to work around this problem, this commit prevents the fast
> path from get_user_pages_fast() from being used on SMP, and directly
^^^^ of?
Else it sounds a bit tautological...

> uses the slow path, which doesn't disable interrupts.
>
> Fixes the following warning when get_futex_key() is called:
>
> WARNING: CPU: 1 PID: 410 at kernel/smp.c:416 smp_call_function_many+0x1fc/0x2ac
> Modules linked in:
>
> CPU: 1 PID: 410 Comm: wdc-pfmu-test Tainted: G O 4.13.0-00035-g0d3023c733a0-dirty #363
> task: 97d9a120 task.stack: 97d2e000
> PC is at smp_call_function_many+0x1fc/0x2ac
> PR is at smp_call_function_many+0x1e2/0x2ac
> PC : 88071fd4 SP : 97d2fcd4 SR : 400080f1
> TEA : c06d6840
> R0 : 000000f0 R1 : 00000002 R2 : 00000000 R3 : 8849c89c
> R4 : 886d62c4 R5 : 886d62c4 R6 : 886db928 R7 : 884a9dec
> R8 : 00000000 R9 : ffffffff R10 : 8844667c R11 : 29ee9000
> R12 : 8844667c R13 : 00000001 R14 : 97d2fcd4
> MACH: 000177e7 MACL: 0000018c GBR : 295742d0 PR : 88071fba
>
> Call trace:
> [<8800fe2c>] sh4_flush_dcache_page+0x0/0xa4
> [<880720a2>] smp_call_function+0x1e/0x50
> [<8800fe2c>] sh4_flush_dcache_page+0x0/0xa4
> [<8800ecc0>] flush_dcache_page+0x34/0x74
> [<88010d1c>] gup_pte_range+0xd0/0x140
> [<88010e04>] gup_pmd_range+0x78/0xa8
> [<88010c4c>] gup_pte_range+0x0/0x140
> [<88011006>] get_user_pages_fast+0xda/0x130
> [<8806f376>] get_futex_key+0x72/0x3a0
> [<8806f6a4>] futex_wait_setup+0x0/0x10c
> [<88055a08>] __rcu_read_unlock+0x0/0x54
> [<880559c8>] __rcu_read_lock+0x0/0x1c
> [<88010f2c>] get_user_pages_fast+0x0/0x130
> [<8806f6de>] futex_wait_setup+0x3a/0x10c
> [<8806f6a4>] futex_wait_setup+0x0/0x10c
> [<8806f852>] futex_wait+0xa2/0x1b8
> [<8806f6a4>] futex_wait_setup+0x0/0x10c
> [<88071c00>] smp_call_function_single+0xac/0x108
> [<8800e908>] cache_noop+0x0/0xc
> [<8800e908>] cache_noop+0x0/0xc
> [<88071018>] do_futex+0x108/0x8f8
> [<880bdfe4>] finish_fault+0x38/0x70
> [<880bdff2>] finish_fault+0x46/0x70
> [<880bf212>] handle_mm_fault+0x2f6/0x954
> [<880bf21a>] handle_mm_fault+0x2fe/0x954
> [<88030e64>] resched_curr+0x54/0x6c
> [<8832be9e>] _raw_spin_lock_irqsave+0xa/0x18
> [<880718dc>] SyS_futex+0xd4/0x124
> [<8801488e>] SyS_clone+0x16/0x24
> [<8800727e>] syscall_call+0x18/0x1e
> [<88071808>] SyS_futex+0x0/0x124
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[...]

MBR, Sergei

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