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linux-next@vger.kernel.org, linux-rt-devel@lists.linux.dev, amd-gfx@lists.freedesktop.org, "# = v7 . 1" , Alex Deucher , Rafal Ostrowski , Mario Limonciello , Sebastian Andrzej Siewior , Thomas Gleixner , spasswwolf@web.de Date: Wed, 29 Jul 2026 19:46:30 +0200 In-Reply-To: References: <20260727105059.75716-1-spasswolf@web.de> <1ead313022bc62dce1f42af9f855727eb9074443.camel@web.de> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: linux-next@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:UXXL9xVFpg84xFCHB0rG+aFtlnKYFsvNaO2LJ6ztbTlTWScBW32 BgWfph7RlZ4Yya/SvHevYKa2i0CsFR2DLiiZNo+A+Ekc0BO0jAoNUxp4jMsIaEnmdmXRYxx 8ItAG/POu3u2BZPBEq0aUsbxKAWboDPu/iM7UrcXx+m8Z66/wPHOA0cq/IAGQw+h/TmUNdG hpETCRAT/v/dPDMgoYlwg== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:+sRb66bWAp8=;RXpZ77x9BO0JodeOZynvb+IqnKE 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+YrIT91w0bSMZExKdm9+FYta/xCSMI/qlHm7JEi3JPgbK6XZ8sApJUDZve3KKE8+76XfHSGdS BwM1aUOc0OTC6h2W9QFGnSCqE5ScN7bLFH+Deb2KuZPEcn2EAW+udlzD+cpi6+VlBdJgRPB+1 HOfe/17DjXWPKNnu+j1vLhFnm6cHVpfkuPXm6F6/CgBVY0zM34EkaVoE5cjzw1cWyUbjP//Gm sdy/5XB2RTXG Am Dienstag, dem 28.07.2026 um 05:51 +0500 schrieb mikhail.v.gavrilov@gmai= l.com: > One thing that may be worth adjusting in the commit message: this is > not only a PREEMPT_RT problem. 183182235f6d was needed on a plain non- > RT x86 kernel. There DC_FP_START() takes fpregs_lock(), which disables > local softirqs, and dc_plane_state is around 335 KiB, so kvzalloc_obj() > falls through to the vmalloc path and hits BUG_ON(in_interrupt()). So > on RT any allocation inside the FPU region is illegal, while on non-RT > it is specifically the large ones - two failure modes, one root cause. I think this was true when commit=C2=A0 183182235f6d ("drm/amd/display: Wrap DCN32 phantom-plane allocation in DC_= RUN_WITH_PREEMPTION_ENABLED") was commited, but commit 04aa71da5f35 ("mm/vmalloc: do not trigger BUG() on BH disabled context") changed the BUG_ON() in __get_vm_area_node(): diff --git a/mm/vmalloc.c b/mm/vmalloc.c index c31a8615a832..bb6ae08d18f5 100644 =2D-- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -3203,7 +3203,7 @@ struct vm_struct *__get_vm_area_node(unsigned long s= ize, struct vm_struct *area; unsigned long requested_size =3D size; =20 - BUG_ON(in_interrupt()); + BUG_ON(in_nmi() || in_hardirq()); size =3D ALIGN(size, 1ul << shift); if (unlikely(!size)) return NULL; so on non-PREEMPT_RT kernels DC_RUN_WITH_PREEMPTION_ENABLED is no longer required for DCN32 phantom-plane allocation. Bert Karwatzki