Messages in this thread | | | From | "Nikita V. Youshchenko" <> | Subject | When it is save to kfree() hrtimer object? | Date | Mon, 7 Dec 2009 10:45:08 +0300 |
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Hi
I'm writing a device driver that processes it's requests.
Each request is described by a request structure. There may be arbitary number of requests pending, so I have a kmem_cache for those objects.
Request processing may include "retry after N usecs" on some conditions, so I have a struct htrimer embedded into my request structure, and use it to implement the delay.
When request processing is complete, I deallocate request structure with kmem_cache_free().
I faced an issue when request processing is complete when running inside hrtimer callback. I have nothing in my request processing that can't be done in atomic context - just several device register accesses and wake_up_interruptible() call. So I thought that I may do everything inside hrtimer callback. Including kmem_cache_free() the request structure.
But looks like I can't. Hrtimer code does access hrtimer object after return from callback, even if HRTIMER_NORESTART is returned. So if request object (that is container of hrtimer object in my case) is deallocated, slab corruption happens.
Looks like I will have to implement some ugly workaround for that ... like a "garbage-collector" thread that will do nothing but deallocate requests from some sort of free list.
I'd like to ask several questions.
- Isn't it a bug that timer object is accessed after it's callback was called and returned HRTIMER_NORESTART?
- If that is not a bug, then when it is "officially safe" to deallocate struct hrtimer object?
- Are there any recommendations on how to implement "single-shot" timers like in my case?
Nikita
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