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a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1727882941; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=YSgt+aBeUQZdrYwlwWCHJ4/usq6jRi1d3IFr2yfT9GI=; b=T7uS2sD+czDLy+KN1Igf/AhTWzSsKa28B0cCvlzyo6D7MBvHiC/x9myr3YzBAKBrT9y4i/ Qe+isxgz/JtitHthNeJicdoRwPqi4/F8Xly3//aLOVsUY+Ktw9cbc47Xnicfz9q7kEtJ7O T/axdsyhf4UBXxjSlrJAzMOv3TIVwdI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1727882941; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=YSgt+aBeUQZdrYwlwWCHJ4/usq6jRi1d3IFr2yfT9GI=; b=ADWlWGVsm0pwzqBpPGn5T+mP4B4sMsHZ0FHZ9EO25rDsTNRkEHS8CJ1eB7nU9mbjri8pDe s61P7q+MGdmJ83AQ== Date: Wed, 2 Oct 2024 17:29:01 +0200 (CEST) From: Miroslav Benes To: Michael Vetter cc: linux-kselftest@vger.kernel.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 3/3] selftests: livepatch: test livepatching a kprobed function In-Reply-To: <20240930093308.65103-4-mvetter@suse.com> Message-ID: References: <20240930093308.65103-1-mvetter@suse.com> <20240930093308.65103-4-mvetter@suse.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.991]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; MID_RHS_MATCH_FROMTLD(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:email] X-Spam-Flag: NO X-Spam-Level: Hi, On Mon, 30 Sep 2024, Michael Vetter wrote: > The test proves that a function that is being kprobed and uses a > post_handler cannot be livepatched. > > Only one ftrace_ops with FTRACE_OPS_FL_IPMODIFY set may be registered > to any given function at a time. > > Signed-off-by: Michael Vetter since my memory is short, I wondered why you need a separate module to register a kprobe for cmdline_proc_show() in vmlinux and why it cannot be achieved through tracefs. So... the test ensures that FTRACE_OPS_FL_IPMODIFY is exclusive. A kprobe sets FTRACE_OPS_FL_IPMODIFY flag if and only if post_handler is not NULL which also indicates a situation when regs->ip may be changed in that kprobe. This is something which cannot be done in tracefs and hence the module. It was not clear to me from the changelog. Miroslav