On Oct 9, 2012, at 4:06 PM, Andrew Morton wrote: > On Sun, 7 Oct 2012 19:06:10 -0700 > Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > >> linux/compiler.h has macros to denote functions that acquire or release >> locks, but not to denote functions called with a lock held that return >> with the lock still held. Add a __must_hold macro to cover that case. > > hum. How does this work? Any code examples and sample sparse output? > Does it apply to all lock types, etc? I accidentally found a bug in sparse where sparse should have been complaining about the locking in the aoe driver's aoenet.c:tx function, which enters with the txlock spinlock held and releases and reacquires it inside a loop. When I modified the loop contents between lock release and acquisition in a patch that I'm preparing now, sparse began complaining about context imbalance. (Before the modifications to the tx function, sparse was exhibiting a bug by *not* complaining.) Here's the complaint: CHECK drivers/block/aoe/aoenet.c /build/ecashin/git/linux/arch/x86/include/asm/spinlock.h:81:9: warning: context imbalance in 'tx' - unexpected unlock CC [M] drivers/block/aoe/aoenet.o ... although I used a smaller file to hone in on the issue when discussing it on the linux-sparse mailing list: http://thread.gmane.org/gmane.comp.parsers.sparse/3091 Josh Triplett suggested I add an annotation telling sparse that the function enters and exits with the lock held, but after reading the sparse man page, where the context feature is described, it looked like that meant specifying a 1 for both parameters: __attribute__((context(x,1,1))), but there was no macro for that. The new patch from Josh Triplett adds the macro that I can use to keep sparse informed about the locking requirements for the tx function. > IOW, where is all this stuff documented? It wasn't real easy to find it, but it's basically something you can infer from reading include/linux/compiler.h and the sparse.1 man page that's included with sparse. I think a brief mention in Documentation/sparse.txt of the relationship between the sparse "context" feature and the locking annotations like __acquires and __must_hold would be a nice addition. I can take a stab at it if folks agree. -- Ed Cashin ecashin@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
