First, an actual, albeit minor, bug: initializing both vmap_info_gen
and vmap_info_cache_gen to 0 marks the cache as valid, which it's not.
vmap_info_gen should be initialized to 1 to force an initial
cache update.
Second, I don't see why you need a 64-bit counter. Seqlocks consider
32 bits (31 bits, actually, the lsbit means "update in progress") quite
a strong enough guarantee.
Third, it seems as though vmap_info_cache_gen is basically a duplicate
of vmap_info_lock.sequence. It should be possible to make one variable
serve both purposes.
You just need a kludge to handle the case of multiple vamp_info updates
between cache updates.
There are two simple ones:
1) Avoid bumping vmap_info_gen unnecessarily. In vmap_unlock(), do
vmap_info_gen = (vmap_info_lock.sequence | 1) + 1;
2) - Make vmap_info_gen a seqcount_t
- In vmap_unlock(), do write_seqcount_barrier(&vmap_info_gen)
- In get_vmalloc_info, inside the seqlock critical section, do
vmap_info_lock.seqcount.sequence = vmap_info_gen.sequence - 1;
(Using the vmap_info_gen.sequence read while validating the
cache in the first place.)
I should try to write an actual patch illustrating this.
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