Messages in this thread Patch in this message | | | Subject | Re: [RESEND][RFC][PATCH] leds: fix oops race in led trigger registration | From | Richard Purdie <> | Date | Thu, 21 Aug 2008 09:06:54 +0100 |
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Hi,
On Thu, 2008-08-21 at 09:17 +0200, Vegard Nossum wrote: > I resubmit this, which was posted a month ago, with no responses from > the maintainer (and no recent fixes in this area either). I have not > tested it myself, but I am reasonably confident that this is an > obviously correct fix. I guess it would not hurt to exercise it as well. > > Zdenek: Have recent kernels also been showing this behaviour? Did the > patch fix the problem for you? You said something about a new issue > showing up, do you think that was related to this patch? > > Also, just one question (since I'm newbie at this): Is it dangerous to > register the &dev_attr_trigger device file before we put the device on > the list or initialize it completely? If so, the initialization should > probably be moved all to the top before the file is made public.
This patch isn't quite right since whilst it fixes one race, it opens up a number of other potential problems. We definitely should have the led listed in leds_list before calling the various functions and the existing init order is correct in that sense.
I suspect your problem is caused by something calling a trigger registration between the point its added to the list and the init_rwsem(). The best solution is to move the init_rwsem() to earlier in the function. Yes, that means some ifdef ugliness but so be it. Could you see whether you still see the problem with the patch below?
Cheers,
Richard
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c index 559a408..c9d8219 100644 --- a/drivers/leds/led-class.c +++ b/drivers/leds/led-class.c @@ -113,6 +113,9 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev) if (rc) goto err_out; +#ifdef CONFIG_LEDS_TRIGGERS + init_rwsem(&led_cdev->trigger_lock); +#endif /* add to the list of leds */ down_write(&leds_list_lock); list_add_tail(&led_cdev->node, &leds_list); @@ -121,8 +124,6 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev) led_update_brightness(led_cdev); #ifdef CONFIG_LEDS_TRIGGERS - init_rwsem(&led_cdev->trigger_lock); - rc = device_create_file(led_cdev->dev, &dev_attr_trigger); if (rc) goto err_out_led_list;
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