On Tue, Jan 08, 2019 at 11:33:39AM -0800, Anatol Pomozov wrote: > Hello folks, > > A bit of context what I am doing. I am trying to port KTSAN (Kernel > Thread Sanitizer) tool to v4.20. That tool tracks shared data usage > and makes sure it is accessed in a thread-safe manner. > > seqlock is a synchronization primitive used by Linux kernel. KTSAN > annotates read_seqbegin()/read_seqretry() and tracks what data been > accessed in its critical section. > > During KTSAN port I found and interesting seqcount usage introduced in > commit 80055dab5de0c8677bc148c4717ddfc753a9148e > > If I read this commit correctly xt_replace_table() does not use > seqlock in a canonical way to specify a critical section. Instead the > code reads the counter and waits until it gets to a specific value.
(gets away from) > Now I want KTSAN to play with this code nicely. I need to tell KTSAN > something like "this raw_read_seqcount() does not start a critical > section, just ignore it". So temporary I introduced > raw_read_seqcount_nocritical() function that is ignored by KTSAN. Is > it a good solution? This code is special enough to just do: READ_ONCE(->sequence) and be done with it. It doesn't need the smp_rmb() or anything else.