Re: [PATCHv4 0/3] Kernel Live Patching

[Jiri Kosina]

On Wed, 26 Nov 2014, Masami Hiramatsu wrote:

> > Note to Steve:
> > Masami's IPMODIFY patch is heading for -next via your tree.  Once it arrives,
> > I'll rebase and make the change to set IPMODIFY.  Do not pull this for -next
> > yet.  This version (v4) is for review and gathering acks.
> 
> BTW, as we discussed IPMODIFY is an exclusive flag. So if we allocate 
> ftrace_ops for each function in each patch, it could be conflict each 
> other.

Yup, this corresponds to what Petr brought up yesterday. There are cases 
where all solutions (kpatch, kgraft, klp) would allocate multiple 
ftrace_ops for a single function entry (think of patching one function 
multiple times in a row).

So it's not as easy as just setting the flag.

> Maybe we need to have another ops hashtable to find such conflict and 
> new handler to handle it.

If I understand your proposal correctly, that would sound like a hackish 
workaround, trying to basically trick the IPMODIFY flag semantics you just 
implemented :)

What I'd propose instead is to make sure that we always have 
just a ftrace_ops per function entry, and only update the pointers there 
as necessary. Fortunately we can do the switch atomically, by making use 
of ->private.

-- 
Jiri Kosina
SUSE Labs
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