Messages in this thread | | | From | Anatol Pomozov <> | Date | Tue, 8 Jan 2019 11:33:39 -0800 | Subject | seqcount usage in xt_replace_table() |
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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.
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?
Or maybe xt_replace_table() can be enhanced? When I hear that something waits until an event happens on all CPUs I think about wait_event() function. Would it be better for xt_replace_table() to introduce an atomic counter that is decremented by CPUs, and the main CPU waits until the counter gets zero?
WDYT?
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