Messages in this thread | | | Date | Mon, 22 Oct 2007 20:45:39 -0700 | From | Pete Zaitcev <> | Subject | Re: [2.4 patch] Port of adutux driver from 2.6 kernel to 2.4. |
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On Fri, 19 Oct 2007 20:40:35 +0300, Vitaliy Ivanov <vitalivanov@gmail.com> wrote:
Hi, Vitaly, I added you on cc: for the 2.6 cleanup. Please double-check what I'm doing there and use it for your 2.4 version. I hope my intentions get clearer with an example. Now, about the specific question:
> Static lock minor_table_mutex is used for minor table structure. > And dev->sem for dev manipulations and that's why for open_count. > If you will simply browse /drivers/usb dir for 2.4 you will see that > such approach is widely used there. > What's not right?
The fundamental reason why you cannot lock a free-able structure with an in-structure lock is this. Imagine thread A locks in order to process a disconnect. Thread B wants to open and waits for the lock. Notice that the struct is not open, so thread A frees it. At this point, thread B is using a freed memory.
The solution is to lock the instance struct dev with dev->mtx, except for the open count, which is locked by a static lock (I'm ignoring interrupts here, which cannot use mutexes).
I'm sorry to say, you're quite right: a number of drivers in 2.4 got it wrong, and some (like adutux) carried it through 2.6.23.
-- Pete - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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