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Tue, 23 Sep 2025 01:30:20 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEW0VkMOIN+fpxJPQSaM1wk6e9xJF4D82MSSPsILxiY2I4mZV59aGE2qlB9thG2n6jd0jvl2g== X-Received: by 2002:a05:600c:4f12:b0:45f:2843:e76d with SMTP id 5b1f17b1804b1-46e1d973866mr18537665e9.4.1758616220301; Tue, 23 Sep 2025 01:30:20 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3f0e28c83d6sm17831553f8f.56.2025.09.23.01.30.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Sep 2025 01:30:19 -0700 (PDT) Message-ID: Subject: Re: [PATCH] rv: Fix wrong type cast in enabled_monitors_next() From: Gabriele Monaco To: Nam Cao , Nathan Chancellor Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 23 Sep 2025 10:30:18 +0200 In-Reply-To: <87tt0t4u19.fsf@yellow.woof> References: <20250806120911.989365-1-namcao@linutronix.de> <20250923002004.GA2836051@ax162> <87tt0t4u19.fsf@yellow.woof> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-09-23 at 07:28 +0200, Nam Cao wrote: > Hi Nathan, >=20 Thanks for finding this! > Nathan Chancellor writes: > > I am seeing a crash when reading from > > /sys/kernel/tracing/rv/enabled_monitors > > on a couple of my arm64 boxes running Fedora after this change, which > > landed in mainline in 6.17-rc7. I can reproduce this in QEMU pretty > > easily. > ... > > With this change reverted, there is no crash. As this change seems to > > have proper justification, is there some other latent bug here? >=20 > Thanks for the report. >=20 > Yes, this patch is broken, because argument 'p' of > enabled_monitors_next() *is* a pointer to struct rv_monitor. I'm not > sure how did I even test this patch... Damn, I'm wondering the same :facepalm: .. > Steven is right, we really need something in kselftest for RV, another th= ing > in my RV TODO list. I can work on that, at least a few selftests for the sysfs, I think this ge= ts the top priority now. >=20 > But reverting is not the real fix, because monitors_show() still expects > a pointer to list_head. Changing monitors_show() is not an option, > because it is shared with the 'available_monitors' interface. >=20 > So the real fix is completely changing the iterator to be list_head > instead of rv_monitor. Looks reasonable, can you work on the fix? I see Steve is out for conferences so this won't be too urgent. Thanks, Gabriele >=20 > Best regards, > Nam >=20 > diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c > index 48338520376f..43e9ea473cda 100644 > --- a/kernel/trace/rv/rv.c > +++ b/kernel/trace/rv/rv.c > @@ -501,7 +501,7 @@ static void *enabled_monitors_next(struct seq_file *m= , > void *p, loff_t *pos) > =C2=A0 > =C2=A0 list_for_each_entry_continue(mon, &rv_monitors_list, list) { > =C2=A0 if (mon->enabled) > - return mon; > + return &mon->list; > =C2=A0 } > =C2=A0 > =C2=A0 return NULL; > @@ -509,7 +509,7 @@ static void *enabled_monitors_next(struct seq_file *m= , > void *p, loff_t *pos) > =C2=A0 > =C2=A0static void *enabled_monitors_start(struct seq_file *m, loff_t *pos= ) > =C2=A0{ > - struct rv_monitor *mon; > + struct list_head *head; > =C2=A0 loff_t l; > =C2=A0 > =C2=A0 mutex_lock(&rv_interface_lock); > @@ -517,15 +517,15 @@ static void *enabled_monitors_start(struct seq_file= *m, > loff_t *pos) > =C2=A0 if (list_empty(&rv_monitors_list)) > =C2=A0 return NULL; > =C2=A0 > - mon =3D list_entry(&rv_monitors_list, struct rv_monitor, list); > + head =3D &rv_monitors_list; > =C2=A0 > =C2=A0 for (l =3D 0; l <=3D *pos; ) { > - mon =3D enabled_monitors_next(m, mon, &l); > - if (!mon) > + head =3D enabled_monitors_next(m, head, &l); > + if (!head) > =C2=A0 break; > =C2=A0 } > =C2=A0 > - return mon; > + return head; > =C2=A0} > =C2=A0 > =C2=A0/*