On Tue, 9 Jan 2007 11:02:35 -0800 (PST) Amit Choudhary wrote: > > --- [EMAIL PROTECTED] wrote: > > > On Mon, 08 Jan 2007 01:06:12 PST, Amit Choudhary said: > > > I do not see how a double free can result in _logical_wrong_behaviour_ of > > > the program and the > > > program keeps on running (like an incoming packet being dropped because > > > of double free). > > Double > > > free will _only_and_only_ result in system crash that can be solved by > > > setting 'x' to NULL. > > > > The problem is that very rarely is there a second free() with no intervening > > use - what actually *happens* usually is: > > > > 1) You alloc the memory > > 2) You use the memory > > 3) You take a reference on the memory, so you know where it is. > > 4) You free the memory > > 5) You use the memory via the reference you took in (3) > > 6) You free it again - at which point you finally know for sure that > > everything in step 5 was doing a fandango on core.... > > > > Correct. And doing kfree(x); x=NULL; is not hiding that. These issues can > still be debugged by > using the slab debugging options. One other benefit of doing this is that if > someone tries to > access the same memory again using the variable 'x', then he will get an > immediate crash. And the > problem can be solved immediately, without using the slab debugging options. > I do not yet > understand how doing this hides the bugs, obfuscates the code, etc. because I > haven't seen an > example yet, but only blanket statements. > > But now I know better, since I haven't heard anything in support of this > case, I have concluded > that doing kfree(x); x=NULL; is _not_needed_ in the "linux kernel". I hope > that no one does it in > the future. And since people vehemently opposed this, I think its better to > add another item on > the kernel janitor's list to remove all the (x=NULL) statements where people > are doing "kfree(x); > x=NULL".
No thanks. If a driver author wants to maintain driver state that way, it's OK, but that doesn't make it a global requirement. --- ~Randy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
