* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Mon, 2009-06-15 at 20:15 +0200, Ingo Molnar wrote: > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > +static int kmap_type_to_context(enum km_type type) > > > +{ > > > + switch (type) { > > > + case KM_BOUNCE_READ: > > > + return KM_CTX_USER; > > > + case KM_SKB_SUNRPC_DATA: > > > + return KM_CTX_USER; > > > + case KM_SKB_DATA_SOFTIRQ: > > > + return KM_CTX_SOFTIRQ; > > > + case KM_USER0: > > > + return KM_CTX_USER; > > > + case KM_USER1: > > > + return KM_CTX_USER; > > > + case KM_BIO_SRC_IRQ: > > > + return KM_CTX_IRQ; > > > + case KM_BIO_DST_IRQ: > > > + return KM_CTX_IRQ; > > > + case KM_PTE0: > > > + return KM_CTX_USER; > > > + case KM_PTE1: > > > + return KM_CTX_USER; > > > + case KM_IRQ0: > > > + return KM_CTX_IRQ; > > > + case KM_IRQ1: > > > + return KM_CTX_IRQ; > > > + case KM_SOFTIRQ0: > > > + return KM_CTX_SOFTIRQ; > > > + case KM_SOFTIRQ1: > > > + return KM_CTX_SOFTIRQ; > > > + case KM_NMI: > > > + return KM_CTX_NMI; > > > + case KM_NMI_PTE: > > > + return KM_CTX_NMI; > > > + } > > > + > > > + return KM_CTX_MAX; > > > > why not do a very simple stack of atomic kmaps, like Hugh suggested? > > > > That would mean a much simpler interface: > > > > kaddr = kmap_atomic(page); > > > > no index needed. The kunmap pops the entry off the stack: > > > > kunmap_atomic(kaddr); > > > > This becomes simpler too. > > > > Now, a stack can be overflown by imbalance - but that's easy to > > detect and existing entries are easily printed and thus the source > > of the leak is easily identified. > > > > In my book this design beats the current enumeration of kmap types > > indices hands down ... It would likely be much more robust as well, > > and much more easy to extend. > > > > Am i missing any subtlety? > > The above is mostly debug code used to validate the kmap_atomic > conditions. > > KM_CTX_NMI nests in KM_CTX_IRQ nests in KM_CTX_SOFTIRQ nests in > KM_CTX_USER. > > And validate that we indeed are in the context specified by the type. > That is, it will warn if we use KM_IRQ1 with KM_CTX_IRQ from user > context. > > Some of this was already captured in the old kmap debug code which I > removed. > > But yes, I should write that nicer.. but ... look at the APIs i propose above. We dont need _any_ 'types'. That type enumeration is basically an open-coded allocator. If we do a _real_ allocator (a balanced stack of atomic kmaps) we dont need any of those indices, and all the potential for mismatch goes away as well - a stack nests trivially with IRQ and NMI and arbitrary other contexts. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html