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[212.8.243.115]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490454ea134sm25438455e9.8.2026.05.21.23.45.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 23:45:59 -0700 (PDT) Message-ID: Subject: Re: [PATCH] Re: Re: [RFC PATCH v2 04/10] rv/da: add pre-allocated storage pool for per-object monitors From: Gabriele Monaco To: Wen Yang Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, rostedt@goodmis.org Date: Fri, 22 May 2026 08:45:57 +0200 In-Reply-To: <7917085b-fef1-4017-b289-eefe84332ff5@linux.dev> References: <668f83581c58644a84cab5e6736864a439bb8e28.camel@redhat.com> <20260515083002.106512-1-gmonaco@redhat.com> <6d2f3490-5e30-4966-a3cd-372a34e10ba2@linux.dev> <5183dc18d63b617ab0f19290e8a790fa6898f372.camel@redhat.com> <7917085b-fef1-4017-b289-eefe84332ff5@linux.dev> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: HR8KQzIr-qZbdtP9HqPdOpTFZBlvDRWJXRk1ERW8ILc_1779432360 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Wen, On Fri, 2026-05-22 at 01:40 +0800, Wen Yang wrote: > Hi Gabriele,=20 >=20 > No specific reason for REL_SOFT =E2=80=94 not intentional, reverting to= =20 > REL_HARD. > =C2=A0 > Reproduced the stall on the same config (PREEMPT_RT +=20 > PROVE_LOCKING/PROVE_RCU).=20 >=20 > Root cause is a cleanup ordering bug in uprobe_detail_waiting.tc,=20 > unrelated to REL_SOFT/REL_HARD: > =C2=A0 >=20 > =C2=A0=C2=A0 # original cleanup =E2=80=94 wrong order=20 >=20 > =C2=A0=C2=A0 echo "-${UPROBE_TARGET}:${start_offset}" > "$TLOB_MONITOR"= =C2=A0 # (A)=20 >=20 > =C2=A0=C2=A0 kill "$hog_pid"=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= # (B)=20 >=20 > =C2=A0 > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (A)= =20 > triggers synchronize_srcu() in the kernel. But tlob_target is stuck=20 > mid-uprobe_notify_resume holding an SRCU read lock, preempted by the=20 > FIFO-99 hog -> so the reader never finishes and (B) is never reached.=20 > rcuc/0 (a kthread on PREEMPT_RT) is also starved by the hog -> RCU stall. great you found the issue and solution. Wonder why lockdep wasn't more informative, but probably the issue was so frequent to hog that too. > =C2=A0=C2=A0 Fix: kill the hog first:=20 > =C2=A0 >=20 > =C2=A0=C2=A0 kill "$hog_pid"; wait "$hog_pid"=20 >=20 > =C2=A0=C2=A0 echo "-${UPROBE_TARGET}:${start_offset}" > "$TLOB_MONITOR"= =20 >=20 >=20 > On the PREEMPT_RT it is more reliably triggered there because rcuc/0 > runs as a preemptible kthread rather than in softirq, making it easier > for the hog to monopolise the CPU long enough to hit the stall. >=20 > Thank you for the thorough review and valuable suggestions. We are=20 > working through all of them and running the full test suite. > We expect to post v3 within the next two days. Alright, sounds good. Thanks, Gabriele