On Tue, 5 May 2009 12:44:01 +0200 Oliver Neukum <oliver@xxxxxxxxxx> wrote: > Am Dienstag, 5. Mai 2009 08:11:57 schrieb Andrew Morton: > > On Mon, 4 May 2009 16:01:51 +0200 Oliver Neukum <oliver@xxxxxxxxxx> wrote: > > > > I want people to be forced to think about memory allocations. > > > We had endless trouble during 2.4 with storage deadlocking. > > > We simply need full control of this. > > > > thou-shalt-use-GFP_NOFS is a very common pattern in many filesystems. > > And thou-shalt-use-GFP_NOIO is a very common pattern in block drivers. > > USB drivers are interface level yet some functions, reset and power > management, are on a device level. As it is unpredictable whether > a driver will share a device with a storage driver, all USB drivers as far as > these functions are concerned must be considered block device drivers. > That's the reason GFP_NOIO is so prevalent in USB. There must be some particular action which flips the thread of control from one state to the other. eg, taking of a lock. > > I wonder how hard it would be to add runtime debugging checks? If > > I'd prefer compile time checks. Ideally we'd annotate a function with an > attribute making the compiler barf if copy_to/from_user or an inappropriate > kmalloc is used. It can't be perfect due to function pointers, but it would > be a good start. I don't think that would have enough coverage - bugs in this area tend to come from calling some function which looks innocent, but which calls some function which calls some function which calls some function which uses GFP_KERNEL. And then there's stuff like "usb takes a mutex which is also taken by some other thread which does a GFP_KERNEL allocation while holding that mutex". -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
