| Message ID | 20180615155237.8166-1-thomas.petazzoni@bootlin.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hello, On Fri, 15 Jun 2018 19:04:45 +0300, Sergei Shtylyov wrote: > 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... I re-read again my sentence, and I believe it's correct and it has the meaning I intended to give. Of course, I'm not a native english speaker, so I might be wrong on this :-) I'm actually more interested in hearing whether there is a better solution to this problem. This patch submission is really a very proposal, and I'm hoping to get some better suggestions on how to approach the problem. Best regards, Thomas
Hello, On Fri, 15 Jun 2018 19:04:45 +0300, Sergei Shtylyov wrote: > 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... Yes, agreed. I can fix that up for a v2, or perhaps such a small typo can be fixed while applying the patches. Could someone review and/or merge those patches ? I sent four patches, which are still pending: [PATCH] arch/sh: kernel: use KERN_CONT in print_sh_insn() [PATCH] arch/sh: kernel: use KERN_CONT in dump_mem() [PATCH] arch/sh: fix SH4 flush_dcache_all() for SMP [PATCH] arch/sh: use slow path for get_user_pages_fast() on SMP Note that this last one is more a workaround than a proper fix. It does the job, but there is very likely a better solution, and I was hoping to get some insights/suggestions. Thanks a lot, Thomas
diff --git a/arch/sh/mm/gup.c b/arch/sh/mm/gup.c index 56c86ca98ecf..075c8efe6c1d 100644 --- a/arch/sh/mm/gup.c +++ b/arch/sh/mm/gup.c @@ -234,6 +234,9 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, if (end < start) goto slow_irqon; + if (IS_ENABLED(CONFIG_SMP)) + goto slow_irqon; + local_irq_disable(); pgdp = pgd_offset(mm, addr); do {
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 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> --- Note: this is really a work around. Perhaps SuperH should use the generic GUP implementation from mm/gup.c ? Any other solution ? arch/sh/mm/gup.c | 3 +++ 1 file changed, 3 insertions(+)