Messages in this thread | | | Date | Sun, 31 Jul 2022 23:48:32 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2] make buffer_locked provide an acquire semantics |
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On Sun, Jul 31, 2022 at 10:30:11AM -0700, Paul E. McKenney wrote: > That said, I confess that I am having a hard time finding the > buffer_locked() definition. So if buffer_locked() uses normal C-language > accesses to sample the BH_Lock bit of the ->b_state field, then yes, > there could be a problem. The compiler would then be free to reorder > calls to buffer_locked() because it could then assume that no other > thread was touching that ->b_state field.
You're having a hard time finding it because it's constructed with the C preprocessor. I really wish we generated header files using CPP once and then included the generated/ file. That would make them greppable.
You're looking for include/linux/buffer_head.h and it's done like this:
enum bh_state_bits { ... BH_Lock, /* Is locked */ ...
#define BUFFER_FNS(bit, name) \ ... static __always_inline int buffer_##name(const struct buffer_head *bh) \ { \ return test_bit(BH_##bit, &(bh)->b_state); \ }
BUFFER_FNS(Lock, locked)
(fwiw, the page/folio versions of these functions don't autogenerate the lock or uptodate ones because they need extra functions called)
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