Re: [RFC 03/16] kgr: initial code

From: Jiri Kosina <jkosina@suse.cz>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jiri Slaby <jslaby@suse.cz>,
	linux-kernel@vger.kernel.org, jirislaby@gmail.com,
	Vojtech Pavlik <vojtech@suse.cz>, Michael Matz <matz@suse.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@redhat.com>
Subject: Re: [RFC 03/16] kgr: initial code
Date: Thu, 1 May 2014 22:37:47 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LNX.2.00.1405012233510.29834@pobox.suse.cz> (raw)
In-Reply-To: <87tx99ckuh.fsf@tassilo.jf.intel.com>

On Thu, 1 May 2014, Andi Kleen wrote:

> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> > index 1e96c3628bf2..a03b1e9d2de3 100644
> > --- a/arch/x86/kernel/entry_64.S
> > +++ b/arch/x86/kernel/entry_64.S
> > @@ -615,6 +615,7 @@ GLOBAL(system_call_after_swapgs)
> >  	movq  %rax,ORIG_RAX-ARGOFFSET(%rsp)
> >  	movq  %rcx,RIP-ARGOFFSET(%rsp)
> >  	CFI_REL_OFFSET rip,RIP-ARGOFFSET
> > +	movw $0, TI_kgr_in_progress+THREAD_INFO(%rsp,RIP-ARGOFFSET)
> 
> Better use 4 bytes. This has the potential to cause an expensive
> Length Changing Prefixes Stall on Intel CPUs.

Patch 16/16 converts this to a single bit within TI_flags.

> > +static int kgr_init_ftrace_ops(const struct kgr_patch_fun *patch_fun)
> > +{
> > +	struct kgr_loc_caches *caches;
> > +	unsigned long fentry_loc;
> > +
> > +	/*
> > +	 * Initialize the ftrace_ops->private with pointers to the fentry
> > +	 * sites of both old and new functions. This is used as a
> > +	 * redirection target in the per-arch stubs.
> > +	 *
> > +	 * Beware! -- freeing (once unloading will be implemented)
> > +	 * will require synchronize_sched() etc.
> > +	 */
> > +
> > +	caches = kmalloc(sizeof(*caches), GFP_KERNEL);
> > +	if (!caches) {
> > +		kgr_debug("kgr: unable to allocate fentry caches\n");
> > +		return -ENOMEM;
> > +	}
> 
> All the error paths in this function leak memory.

Gah, good catch, thanks a lot.

-- 
Jiri Kosina
SUSE Labs