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Sun, 06 Sep 2026 13:23:00 -0700 (PDT) From: Ivy Lopez To: sathya.prakash@broadcom.com, sreekanth.reddy@broadcom.com, suganath-prabu.subramani@broadcom.com, ranjan.kumar@broadcom.com, James.Bottomley@HansenPartnership.com, martin.petersen@oracle.com Cc: MPT-FusionLinux.pdl@broadcom.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Ivy Lopez Subject: [PATCH] scsi: mpt3sas: fix nr_msix underflow in _base_assign_reply_queues() Date: Sun, 6 Sep 2026 14:22:50 -0600 Message-ID: <20260906202250.53653-1-skunkolee@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The fallback path incorrectly subtracts iopoll_q_count when computing nr_msix, when the intent is to reserve both high_iops_queues and iopoll_q_count reply queues from the round-robin pool. Since iopoll_q_count can be positive, the current subtraction inflates nr_msix instead of reducing it, leaving far more queues in the round-robin pool than actually available once high-iops and iopoll queues are accounted for. Beyond producing an incorrect grouping of cpus onto msix vectors, the corrected formula can still drive nr_msix to zero or below under plausible queue configurations (verified arithmetically), which would either wrap to a large unsigned value and silently break affinity grouping, or hit a divide-by-zero in the following nr_cpus / nr_msix computation. Add an explicit check for nr_msix == 0 and also warn if the reply queue budget is exhausted. Fixes: 432bc7caef4e ("scsi: mpt3sas: Add io_uring iopoll support") Signed-off-by: Ivy Lopez --- drivers/scsi/mpt3sas/mpt3sas_base.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c index ce5a5882acc8..31b80ed6ddec 100644 --- a/drivers/scsi/mpt3sas/mpt3sas_base.c +++ b/drivers/scsi/mpt3sas/mpt3sas_base.c @@ -3275,7 +3275,11 @@ _base_assign_reply_queues(struct MPT3SAS_ADAPTER *ioc) fall_back: cpu = cpumask_first(cpu_online_mask); - nr_msix -= (ioc->high_iops_queues - iopoll_q_count); + nr_msix -= (ioc->high_iops_queues + iopoll_q_count); + if (!nr_msix) { + ioc_warn(ioc, "high_iops_queues and iopoll_q_count exceed available MSI-X vectors\n"); + return; + } index = 0; list_for_each_entry(reply_q, &ioc->reply_queue_list, list) { -- 2.55.0