Re: [PATCH] video: fbdev: pm2fb: avoid stall on fb_sync
From: Randy Dunlap <hidden>
Date: 2021-02-20 23:34:53
Also in:
dri-devel, lkml
Hi-- On 2/20/21 3:02 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.
Is this a real problem or theoretical? Does someone still use this driver?
quoted hunk ↗ jump to hunk
Signed-off-by: Tong Zhang <redacted> --- 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..8578c64a0c54 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 int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
drop void ^^^ It's already "int". Did you compile this?
+{
+ int timeout = 10000;
+ while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) {
+ cpu_relax();
+ if (--timeout==0)spaces around ==
quoted hunk ↗ jump to hunk
+ 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)
spaces around ==
+ goto end; + } + if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC)) + break; + } while (--timeout_sync>0);
spaces around >
+end: + if ((!timeout_sync) || (!timeout_fifo)) + printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n"); return 0; }
thanks. -- ~Randy