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 --- v3: initialize timeout_fifo to 0, and added comment for WAIT_FIFO_TIMEOUT v2: fix typo and add console log according to Randy's rdunlap@infradead.org comment drivers/video/fbdev/pm2fb.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-)
diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c index 27893fa139b0..37db7e740221 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -183,12 +183,24 @@ 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 +1043,27 @@ 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 = 0;
- 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; }