Re: seqcount usage in xt_replace_table()

[Andrea Parri]

> For seqcounts we currently simply ignore all accesses within the read
> section (thus the requirement to dynamically track read sections).
> What does LKMM say about seqlocks?

LKMM does not currently model seqlocks, if that's what you're asking;
c.f., tools/memory-model/linux-kernel.def for a list of the currently
supported synchronization primitives.

LKMM has also no notion of "data race", it insists that the code must
contain no unmarked accesses; we have been discussing such extensions
since at least Dec'17 (we're not quite there!, as mentioned by Paul).

My opinion is that ignoring all accesses within a given read section
_can_ lead to false negatives (in every possible definition of "data
race" and "read sections" I can think of at the moment ;D):

	P0				P1
	read_seqbegin()			x = 1;
	r0 = x;
	read_seqretry() // =0

ought to be "racy"..., right?  (I didn't audit all the callsites for
read_{seqbegin,seqretry}(), but I wouldn't be surprised to find such
pattern ;D ... "legacy", as you recalled).

  Andrea