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Date: Wed, 3 Mar 2010 22:54:02 +0100 From: Pavel Machek <pavel@....cz> To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> Cc: cl@...ux-foundation.org, linux-kernel@...r.kernel.org Subject: Re: [RFC][PATCH] mm: Remove ZERO_SIZE_PTR. Hi! > > > Everybody should check for ptr != NULL, and most callers are actually checking > > > for ptr != NULL. But nobody is checking for ptr != ZERO_SIZE_PTR. > > > > That is so intentionally because some kernel subsystem can do a zero size > > allocation. > > > So, not only users *can* do zero size allocation, > but also there *are* users who are intentionally doing zero size allocation. > Then, we can't remove ZERO_SIZE_PTR. > > > > Yes, this is the fault of caller. But ZERO_SIZE_PTR is too small value to > > > distinguish "NULL pointer dereference" and "ZERO_SIZE_PTR dereference" because > > > address printed by oops message can easily exceed ZERO_SIZE_PTR when > > > "struct foo" is large. > > > > Correct. > > Maybe PAGE_SIZE / 2 is better than 16? Actually maybe 1 is better than 16? It is 'nicer' number, and <= ZERO_SIZE_PTR will actually be correct. Accessing field it struct will also be easy to differentiate from NULL pointer -- as most members are word aligned... -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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