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Message-ID: <20250826081904.GB87@bytedance> References: <20250826075743.19106-1-xupengbo@oppo.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250826075743.19106-1-xupengbo@oppo.com> On Tue, Aug 26, 2025 at 03:57:42PM +0800, xupengbo wrote: > When a task is migrated out, there is a probability that the tg->load_avg > value will become abnormal. The reason is as follows. > > 1. Due to the 1ms update period limitation in update_tg_load_avg(), there > is a possibility that the reduced load_avg is not updated to tg->load_avg > when a task migrates out. > 2. Even though __update_blocked_fair() traverses the leaf_cfs_rq_list and > calls update_tg_load_avg() for cfs_rqs that are not fully decayed, the key > function cfs_rq_is_decayed() does not check whether > cfs->tg_load_avg_contrib is null. Consequently, in some cases, > __update_blocked_fair() removes cfs_rqs whose avg.load_avg has not been > updated to tg->load_avg. > > I added a check of cfs_rq->tg_load_avg_contrib in cfs_rq_is_decayed(), > which blocks the case (2.) mentioned above. > After some preliminary discussion and analysis, I think it is feasible to > directly check if cfs_rq->tg_load_avg_contrib is 0 in cfs_rq_is_decay(). > So patch v3 was submitted. > > Fixes: 1528c661c24b ("sched/fair: Ratelimit update to tg->load_avg") > Signed-off-by: xupengbo With the below typo fixed: Tested-by: Aaron Lu Reviewed-by: Aaron Lu > --- > Changes: > v1 -> v2: > - Another option to fix the bug. Check cfs_rq->tg_load_avg_contrib in > cfs_rq_is_decayed() to avoid early removal from the leaf_cfs_rq_list. > - Link to v1 : https://lore.kernel.org/cgroups/20250804130326.57523-1-xupengbo@oppo.com/ > v2 -> v3: > - Check if cfs_rq->tg_load_avg_contrib is 0 derectly. > - Link to v2 : https://lore.kernel.org/cgroups/20250805144121.14871-1-xupengbo@oppo.com/ > > Please send emails to a different email address > after September 3, 2025, after that date will expire > for personal reasons. > > Thanks, > Xu Pengbo > > kernel/sched/fair.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index b173a059315c..df348cb6a5f3 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4062,6 +4062,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) > if (child_cfs_rq_on_list(cfs_rq)) > return false; > > + if (cfs_rq->tg_laod_avg_contrib) ~~~~ typo: tg_load_avg_contrib > + return false; > + > return true; > } > > > base-commit: fab1beda7597fac1cecc01707d55eadb6bbe773c > -- > 2.43.0 >