On 18/12/14 15:55, Martin Jackson wrote: > Dear fbdev developers, > > This relates to the core implementation of fbdev with the > CONFIG_FB_DEFERRED_IO option enabled. > > I believe I have found a bug when doing msync(2) on a framebuffer > device. We are using an old (2.6.37) kernel on an embedded plaform, > but if I look at the current torvalds kernel (fbdev kernel looks > rather old!?), the bug seems to still be there. > > When looking at the msync(2) man page, msync is meant to return 0 on > success and -1 on failure, however we are seeing it return 1, which is > undocumented and in my opinion wrong. > > This is because the fb_deferred_io_fsync method returns the code from > 'schedule_delayed_work', which is either 0 or 1 depending on whether > the work was already scheduled, leading to the possibility that msync > returns the value 1 to userland. Indeed, looks broken. schedule_delayed_work() never returns an error, it just returns a bool telling if the work was already scheduled. I guess no one really uses deferred io much =). Here's a patch: From 9cc80b3cf9d6023ede084d024ed8b5c0cb247bc2 Mon Sep 17 00:00:00 2001 From: Tomi Valkeinen <tomi.valkeinen@xxxxxx> Date: Fri, 19 Dec 2014 13:55:41 +0200 Subject: [PATCH] video/fbdev: fix defio's fsync fb_deferred_io_fsync() returns the value of schedule_delayed_work() as an error code, but schedule_delayed_work() does not return an error. It returns true/false depending on whether the work was already queued. Fix this by ignoring the return value of schedule_delayed_work(). Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx> --- drivers/video/fbdev/core/fb_defio.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 900aa4ecd617..d6cab1fd9a47 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c @@ -83,9 +83,10 @@ int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy cancel_delayed_work_sync(&info->deferred_work); /* Run it immediately */ - err = schedule_delayed_work(&info->deferred_work, 0); + schedule_delayed_work(&info->deferred_work, 0); mutex_unlock(&inode->i_mutex); - return err; + + return 0; } EXPORT_SYMBOL_GPL(fb_deferred_io_fsync); -- 2.2.0
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