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/sVeTUtysUt9PAWdc5ESx/pzD6++7+zK7nn+j4+c074aCnOw57XxGv/boOOVNrmOeSHVpKWmRwu SUBeLLbM4p9oQqEqzv0NdUikesB3fAet1TNKsfmisqjRKNe0tUZ6ZSERmbFb144h+HPhi9GkUsB eSnRvEQaAOYdkOBZCAxCMyrS9K0dyu2GFMm1ApbGZa28hk9lFS/wsuHbNbjJ7jW7DelJ93b/HB+ ExCa0tJqR2GgQHNNn1ok3/Mfyt/ZGU0xG2Dt01kq1jhAamL9vLdVo4fSKNu/b6KS1NG4HMSm6Gr 3Pgv33JyIq6kfTVQ2cVPUgxiQQDfww== X-Proofpoint-GUID: GWpIHw_R6EdMf0fXi7_4h8_Mx-XvmjJ0 X-Authority-Analysis: v=2.4 cv=IciHWXqa c=1 sm=1 tr=0 ts=68b1842d b=1 cx=c_pps a=e1sVV491RgrpLwSTMOnk8w==:117 a=e1sVV491RgrpLwSTMOnk8w==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=2OwXVqhp2XgA:10 a=GoEa3M9JfhUA:10 a=yPCof4ZbAAAA:8 a=pGLkceISAAAA:8 a=IyrIm8NlDI8fC1_FnIcA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 cc=ntf awl=host:13602 On Fri, Aug 29, 2025 at 11:15:17AM +0800, Yafang Shao wrote: > On Thu, Aug 28, 2025 at 6:51 PM Lorenzo Stoakes > wrote: > > > > On Wed, Aug 27, 2025 at 02:50:36PM -0700, Andrii Nakryiko wrote: > > > On Wed, Aug 27, 2025 at 8:48 AM Lorenzo Stoakes > > > wrote: > > > > > > > > On Tue, Aug 26, 2025 at 03:19:41PM +0800, Yafang Shao wrote: > > > > > We will utilize this new kfunc bpf_mm_get_task() to retrieve the > > > > > associated task_struct from the given @mm. The obtained task_struct must > > > > > be released by calling bpf_task_release() as a paired operation. > > > > > > > > You're basically describing the patch you're not saying why - yeah you're > > > > getting a task struct from an mm (only if CONFIG_MEMCG which you don't > > > > mention here), but not for what purpose you intend to use this? > > > > > > > > > > > > > > Signed-off-by: Yafang Shao > > > > > --- > > > > > mm/bpf_thp.c | 34 ++++++++++++++++++++++++++++++++++ > > > > > 1 file changed, 34 insertions(+) > > > > > > > > > > diff --git a/mm/bpf_thp.c b/mm/bpf_thp.c > > > > > index b757e8f425fd..46b3bc96359e 100644 > > > > > --- a/mm/bpf_thp.c > > > > > +++ b/mm/bpf_thp.c > > > > > @@ -205,11 +205,45 @@ __bpf_kfunc void bpf_put_mem_cgroup(struct mem_cgroup *memcg) > > > > > #endif > > > > > } > > > > > > > > > > +/** > > > > > + * bpf_mm_get_task - Get the task struct associated with a mm_struct. > > > > > + * @mm: The mm_struct to query > > > > > + * > > > > > + * The obtained task_struct must be released by calling bpf_task_release(). > > > > > > > > Hmmm so now bpf programs can cause kernel bugs by keeping a reference around? > > > > > > BPF verifier will reject any program that cannot guarantee that > > > bpf_task_release() will always be called. So there shouldn't be any > > > problem here. > > > > Ah that's nice! > > > > What specifically here is enforcing that? Apologies again - BPF is new to me. > > The KF_ACQUIRE and KF_RELEASE flags enforce resource management. If a > BPF helper function (e.g., bpf_mm_get_task()) is marked with > KF_ACQUIRE, the pointer it returns must be released by a corresponding > helper marked with KF_RELEASE (e.g., bpf_task_release()). The BPF > verifier will reject any program that fails to pair these calls > correctly. OK that's really really nice actually! :) Thanks! > > -- > Regards > Yafang Cheers, Lorenzo