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McKenney" Subject: Re: [PATCH] tracing: fprobe: fix suspicious rcu usage in fprobe_entry Message-ID: <20250828222357.55fab4c2@batman.local.home> In-Reply-To: <20250829021436.19982-1-dongml2@chinatelecom.cn> References: <20250829021436.19982-1-dongml2@chinatelecom.cn> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: ima4r3ynrjku7c7wbsowqez1ui5yugaf X-Rspamd-Server: rspamout07 X-Rspamd-Queue-Id: 8C5916000B X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/Um7o/xuj05SM+I7zwu49yDvaXP8UURTk= X-HE-Tag: 1756434238-941031 X-HE-Meta: U2FsdGVkX1+FHbgTP4MfqSCwG9uihNP6dP7ItW+sZr3ePzAx9HQ5c+Dgw8J/7OPRXZ3Nu4Y6JNJ/ds01+7jSZBhERC0W9TOk12MTo+zFRJ8vutOg3L7m8dKYaqV5FKtFHp5M4RTxk4RkLzenmiB+lXj5TNija+K6C4ibVSZYmL3tdvltH7s1szI246tiQXD1P2POJrt2pPbwEjR9NbeWHJ5ZFNulVL8PA0RYriESOUMyyL7OafSjKSWN8V8e4H1lpSGZsSA4foxdnIMB+75Lbd31mCqOmQF5NtsbRWG0OE/+5lKu0CCr56wujU2BDVG6iG/111qDS4SBgxfCQFoWu/zvIA2WQ1doiUppHLL4tv9+sjsCr14yLw== On Fri, 29 Aug 2025 10:14:36 +0800 Menglong Dong wrote: > rcu_read_lock() is not needed in fprobe_entry, but rcu_dereference_check() > is used in rhltable_lookup(), which causes suspicious RCU usage warning: > > WARNING: suspicious RCU usage > 6.17.0-rc1-00001-gdfe0d675df82 #1 Tainted: G S > ----------------------------- > include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage! > ...... > stack backtrace: > CPU: 1 UID: 0 PID: 4652 Comm: ftracetest Tainted: G S > Tainted: [S]=CPU_OUT_OF_SPEC, [I]=FIRMWARE_WORKAROUND > Hardware name: Dell Inc. OptiPlex 7040/0Y7WYT, BIOS 1.1.1 10/07/2015 > Call Trace: > > dump_stack_lvl+0x7c/0x90 > lockdep_rcu_suspicious+0x14f/0x1c0 > __rhashtable_lookup+0x1e0/0x260 > ? __pfx_kernel_clone+0x10/0x10 > fprobe_entry+0x9a/0x450 > ? __lock_acquire+0x6b0/0xca0 > ? find_held_lock+0x2b/0x80 > ? __pfx_fprobe_entry+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ? lock_acquire+0x14c/0x2d0 > ? __might_fault+0x74/0xc0 > function_graph_enter_regs+0x2a0/0x550 > ? __do_sys_clone+0xb5/0x100 > ? __pfx_function_graph_enter_regs+0x10/0x10 > ? _copy_to_user+0x58/0x70 > ? __pfx_kernel_clone+0x10/0x10 > ? __x64_sys_rt_sigprocmask+0x114/0x180 > ? __pfx___x64_sys_rt_sigprocmask+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ftrace_graph_func+0x87/0xb0 > > Fix this by using rcu_read_lock() for rhltable_lookup(). Alternatively, we > can use rcu_lock_acquire(&rcu_lock_map) here to obtain better performance. > However, it's not a common usage :/ So this is needed even though it's called under preempt_disable(). Paul, do we need to add an rcu_read_lock() because the code in rht (rhashtable) requires RCU read lock? I thought that rcu_read_lock() and preempt_disable() have been merged? -- Steve > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202508281655.54c87330-lkp@intel.com > Fixes: dfe0d675df82 ("tracing: fprobe: use rhltable for fprobe_ip_table") > Signed-off-by: Menglong Dong > --- > kernel/trace/fprobe.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index fb127fa95f21..fece0f849c1c 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -269,7 +269,9 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops, > if (WARN_ON_ONCE(!fregs)) > return 0; > > + rcu_read_lock(); > head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params); > + rcu_read_unlock(); > reserved_words = 0; > rhl_for_each_entry_rcu(node, pos, head, hlist) { > if (node->addr != func)