| Message ID | 20210221000024.358772-1-ztong0001@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] video: fbdev: pm2fb: avoid stall on fb_sync | expand |
On 2/20/21 4:00 PM, Tong Zhang wrote: > pm2fb_sync is called when doing /dev/fb read or write. > The original pm2fb_sync wait indefinitely on hardware flags which can > possibly stall kernel and make everything unresponsive. > Instead of waiting indefinitely, we can timeout to give user a chance to > get back control. > > [ 39.503356] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-48-gd9c812dda5194 > [ 39.503947] Call Trace: > [ 39.504081] <IRQ> > [ 39.504193] dump_stack+0x7d/0xa3 > [ 39.504377] nmi_cpu_backtrace.cold+0x32/0x7e > [ 39.504613] ? lapic_can_unplug_cpu+0x70/0x70 > [ 39.504850] nmi_trigger_cpumask_backtrace+0xdf/0x100 > [ 39.505121] rcu_dump_cpu_stacks+0xed/0x130 > [ 39.505349] rcu_sched_clock_irq.cold+0x3b1/0x61d > [ 39.505602] ? hrtimer_run_queues+0x2c/0x1b0 > [ 39.505833] ? __acct_update_integrals+0x136/0x160 > [ 39.506091] update_process_times+0xb9/0xf0 > [ 39.506317] tick_sched_handle.isra.0+0x5c/0x80 > [ 39.506562] tick_sched_timer+0x70/0x90 > [ 39.506770] __hrtimer_run_queues+0x1c6/0x3e0 > [ 39.517095] ? tick_sched_handle.isra.0+0x80/0x80 > [ 39.517349] ? enqueue_hrtimer+0xd0/0xd0 > [ 39.517561] ? _raw_write_lock_irqsave+0xd0/0xd0 > [ 39.517812] ? ktime_get+0x45/0xb0 > [ 39.517997] ? ktime_get_update_offsets_now+0x96/0x150 > [ 39.518273] hrtimer_interrupt+0x1a0/0x340 > [ 39.518496] __sysvec_apic_timer_interrupt+0x7f/0x160 > [ 39.518768] asm_call_irq_on_stack+0xf/0x20 > [ 39.518997] </IRQ> > [ 39.519114] sysvec_apic_timer_interrupt+0x6f/0x80 > [ 39.519372] asm_sysvec_apic_timer_interrupt+0x12/0x20 > [ 39.519647] RIP: 0010:pm2fb_sync+0x47/0x70 [pm2fb] > [ 39.519907] Code: 89 ef e8 0c 87 2c c1 48 8b 53 08 31 c0 89 82 40 8c 00 00 0f ae f0 48 8b 53 08 1 > [ 39.520885] RSP: 0018:ffff88810a1f7df8 EFLAGS: 00000202 > [ 39.521165] RAX: 0000000072d5d49f RBX: ffff88810a034418 RCX: ffffc900000b0020 > [ 39.521542] RDX: ffffc900000b0000 RSI: 0000000000000246 RDI: ffff88810a034420 > [ 39.521920] RBP: ffff88810a034420 R08: 0000000000000000 R09: ffffed102143ef64 > [ 39.522297] R10: 0000000000000003 R11: ffffed102143ef63 R12: ffff88810a1f7ed0 > [ 39.522673] R13: ffff88810a034000 R14: ffffc90002800000 R15: ffff888109e5e000 > [ 39.523053] ? pm2fb_sync+0x24/0x70 [pm2fb] > [ 39.523280] fb_write+0x1c2/0x2d0 > [ 39.523461] vfs_write+0x108/0x380 > [ 39.523647] ksys_write+0xb4/0x150 > [ 39.523832] ? __ia32_sys_read+0x40/0x40 > [ 39.524043] ? fpregs_assert_state_consistent+0x4d/0x60 > [ 39.524322] do_syscall_64+0x33/0x40 > [ 39.524517] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > [ 39.524788] RIP: 0033:0x7f5e50097970 > [ 39.524981] Code: 73 01 c3 48 8b 0d 28 d5 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 4 > [ 39.525952] RSP: 002b:00007ffec6895b38 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > [ 39.526352] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5e50097970 > [ 39.526726] RDX: 0000000000000200 RSI: 000056491a6ad000 RDI: 0000000000000001 > [ 39.537261] RBP: 0000000000000200 R08: 0000000000000000 R09: 000056491a6ad030 > [ 39.537633] R10: 0000000000000871 R11: 0000000000000246 R12: 0000000000000800 > [ 39.538008] R13: 000056491a6ad000 R14: 0000000000000200 R15: 0000000000000000 > > Signed-off-by: Tong Zhang <ztong0001@gmail.com> > --- > v2: fix typo and add console log according to Randy's <rdunlap@infradead.org> comment > > drivers/video/fbdev/pm2fb.c | 29 ++++++++++++++++++++++++++--- > 1 file changed, 26 insertions(+), 3 deletions(-) > > diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c > index 27893fa139b0..d6731e04252f 100644 > --- a/drivers/video/fbdev/pm2fb.c > +++ b/drivers/video/fbdev/pm2fb.c > @@ -183,12 +183,23 @@ static inline void pm2v_RDAC_WR(struct pm2fb_par *p, s32 idx, u32 v) > > #ifdef CONFIG_FB_PM2_FIFO_DISCONNECT > #define WAIT_FIFO(p, a) > +#define WAIT_FIFO_TIMEOUT(p, a) (0) > #else > static inline void WAIT_FIFO(struct pm2fb_par *p, u32 a) > { > while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) > cpu_relax(); > } /* return 1 for timeout, otherwise 0 */ > +static inline int WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a) > +{ > + int timeout = 10000; > + while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) { > + cpu_relax(); > + if (--timeout == 0) > + return 1; > + } > + return 0; > +} > #endif > > /* > @@ -1031,15 +1042,27 @@ static int pm2fb_blank(int blank_mode, struct fb_info *info) > static int pm2fb_sync(struct fb_info *info) > { > struct pm2fb_par *par = info->par; > + int timeout_sync = 10000; > + int timeout_fifo; > > - WAIT_FIFO(par, 1); > + if (WAIT_FIFO_TIMEOUT(par, 1)) > + goto end; if the above goto happens, timeout_fifo is used but not initialized at label end: > pm2_WR(par, PM2R_SYNC, 0); > mb(); > do { > - while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) > + timeout_fifo = 10000; > + while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) { > cpu_relax(); > - } while (pm2_RD(par, PM2R_OUT_FIFO) != PM2TAG(PM2R_SYNC)); > + if (--timeout_fifo == 0) > + goto end; > + } > + if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC)) > + break; > + } while (--timeout_sync > 0); > > +end: > + if ((!timeout_sync) || (!timeout_fifo)) > + printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n"); > return 0; > } > > I suppose the rest of the patch is OK since it works for you. I don't know any of this code. It would be nice to know what some of those pm2_RD(par, SOME_REG) mean so that I could sort of understand what it is doing, but don't go spending time on it just for me. It's not worth doing that IMO.
On Sat, Feb 20, 2021 at 7:36 PM Randy Dunlap <rdunlap@infradead.org> wrote: > I suppose the rest of the patch is OK since it works for you. > > I don't know any of this code. It would be nice to know what some > of those pm2_RD(par, SOME_REG) mean so that I could sort of > understand what it is doing, but don't go spending time on it > just for me. It's not worth doing that IMO. > > > -- > ~Randy Thank you Randy. I have sent another revision. I am also curious about those registers -- but it is hard to accurately figure it out without datasheet -- my speculation is that it calls the device to do some sort of frame buffer synchronizations here Thanks, - Tong
diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c index 27893fa139b0..d6731e04252f 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -183,12 +183,23 @@ static inline void pm2v_RDAC_WR(struct pm2fb_par *p, s32 idx, u32 v) #ifdef CONFIG_FB_PM2_FIFO_DISCONNECT #define WAIT_FIFO(p, a) +#define WAIT_FIFO_TIMEOUT(p, a) (0) #else static inline void WAIT_FIFO(struct pm2fb_par *p, u32 a) { while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) cpu_relax(); } +static inline int WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a) +{ + int timeout = 10000; + while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) { + cpu_relax(); + if (--timeout == 0) + return 1; + } + return 0; +} #endif /* @@ -1031,15 +1042,27 @@ static int pm2fb_blank(int blank_mode, struct fb_info *info) static int pm2fb_sync(struct fb_info *info) { struct pm2fb_par *par = info->par; + int timeout_sync = 10000; + int timeout_fifo; - WAIT_FIFO(par, 1); + if (WAIT_FIFO_TIMEOUT(par, 1)) + goto end; pm2_WR(par, PM2R_SYNC, 0); mb(); do { - while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) + timeout_fifo = 10000; + while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) { cpu_relax(); - } while (pm2_RD(par, PM2R_OUT_FIFO) != PM2TAG(PM2R_SYNC)); + if (--timeout_fifo == 0) + goto end; + } + if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC)) + break; + } while (--timeout_sync > 0); +end: + if ((!timeout_sync) || (!timeout_fifo)) + printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n"); return 0; }
pm2fb_sync is called when doing /dev/fb read or write. The original pm2fb_sync wait indefinitely on hardware flags which can possibly stall kernel and make everything unresponsive. Instead of waiting indefinitely, we can timeout to give user a chance to get back control. [ 39.503356] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-48-gd9c812dda5194 [ 39.503947] Call Trace: [ 39.504081] <IRQ> [ 39.504193] dump_stack+0x7d/0xa3 [ 39.504377] nmi_cpu_backtrace.cold+0x32/0x7e [ 39.504613] ? lapic_can_unplug_cpu+0x70/0x70 [ 39.504850] nmi_trigger_cpumask_backtrace+0xdf/0x100 [ 39.505121] rcu_dump_cpu_stacks+0xed/0x130 [ 39.505349] rcu_sched_clock_irq.cold+0x3b1/0x61d [ 39.505602] ? hrtimer_run_queues+0x2c/0x1b0 [ 39.505833] ? __acct_update_integrals+0x136/0x160 [ 39.506091] update_process_times+0xb9/0xf0 [ 39.506317] tick_sched_handle.isra.0+0x5c/0x80 [ 39.506562] tick_sched_timer+0x70/0x90 [ 39.506770] __hrtimer_run_queues+0x1c6/0x3e0 [ 39.517095] ? tick_sched_handle.isra.0+0x80/0x80 [ 39.517349] ? enqueue_hrtimer+0xd0/0xd0 [ 39.517561] ? _raw_write_lock_irqsave+0xd0/0xd0 [ 39.517812] ? ktime_get+0x45/0xb0 [ 39.517997] ? ktime_get_update_offsets_now+0x96/0x150 [ 39.518273] hrtimer_interrupt+0x1a0/0x340 [ 39.518496] __sysvec_apic_timer_interrupt+0x7f/0x160 [ 39.518768] asm_call_irq_on_stack+0xf/0x20 [ 39.518997] </IRQ> [ 39.519114] sysvec_apic_timer_interrupt+0x6f/0x80 [ 39.519372] asm_sysvec_apic_timer_interrupt+0x12/0x20 [ 39.519647] RIP: 0010:pm2fb_sync+0x47/0x70 [pm2fb] [ 39.519907] Code: 89 ef e8 0c 87 2c c1 48 8b 53 08 31 c0 89 82 40 8c 00 00 0f ae f0 48 8b 53 08 1 [ 39.520885] RSP: 0018:ffff88810a1f7df8 EFLAGS: 00000202 [ 39.521165] RAX: 0000000072d5d49f RBX: ffff88810a034418 RCX: ffffc900000b0020 [ 39.521542] RDX: ffffc900000b0000 RSI: 0000000000000246 RDI: ffff88810a034420 [ 39.521920] RBP: ffff88810a034420 R08: 0000000000000000 R09: ffffed102143ef64 [ 39.522297] R10: 0000000000000003 R11: ffffed102143ef63 R12: ffff88810a1f7ed0 [ 39.522673] R13: ffff88810a034000 R14: ffffc90002800000 R15: ffff888109e5e000 [ 39.523053] ? pm2fb_sync+0x24/0x70 [pm2fb] [ 39.523280] fb_write+0x1c2/0x2d0 [ 39.523461] vfs_write+0x108/0x380 [ 39.523647] ksys_write+0xb4/0x150 [ 39.523832] ? __ia32_sys_read+0x40/0x40 [ 39.524043] ? fpregs_assert_state_consistent+0x4d/0x60 [ 39.524322] do_syscall_64+0x33/0x40 [ 39.524517] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 39.524788] RIP: 0033:0x7f5e50097970 [ 39.524981] Code: 73 01 c3 48 8b 0d 28 d5 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 4 [ 39.525952] RSP: 002b:00007ffec6895b38 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 39.526352] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5e50097970 [ 39.526726] RDX: 0000000000000200 RSI: 000056491a6ad000 RDI: 0000000000000001 [ 39.537261] RBP: 0000000000000200 R08: 0000000000000000 R09: 000056491a6ad030 [ 39.537633] R10: 0000000000000871 R11: 0000000000000246 R12: 0000000000000800 [ 39.538008] R13: 000056491a6ad000 R14: 0000000000000200 R15: 0000000000000000 Signed-off-by: Tong Zhang <ztong0001@gmail.com> --- v2: fix typo and add console log according to Randy's <rdunlap@infradead.org> comment drivers/video/fbdev/pm2fb.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-)