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Sun, 12 Jul 2026 14:37:35 -0700 (PDT) From: Rosen Penev To: linux-ide@vger.kernel.org Cc: Damien Le Moal , Niklas Cassel , Jeff Garzik , Mark Miesfeld , Rupjyoti Sarmah , Prodyut Hazarika , linux-kernel@vger.kernel.org (open list) Subject: [PATCHv4 4/4] ata: sata_dwc_460ex: fix infinite loop in NCQ tag completion bit-scanning Date: Sun, 12 Jul 2026 14:37:28 -0700 Message-ID: <20260712213728.824420-5-rosenp@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260712213728.824420-1-rosenp@gmail.com> References: <20260712213728.824420-1-rosenp@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The hand-rolled bit-scanning loop in the NCQ completion path has an infinite loop bug. When tag_mask has only high bits set (e.g. 0x80000000), the inner while loop left-shifts tag_mask until it overflows to 0. At that point !(0 & 1) is always true and 0 <<= 1 stays 0, causing an infinite loop in hardirq context with a spinlock held. Replace the open-coded bit-scanning with __ffs() which correctly finds the least significant set bit and is bounded by the width of the argument. Fixes: 62936009f35a ("[libata] Add 460EX on-chip SATA driver, sata_dwc_460ex") Assisted-by: opencode:big-pickle Signed-off-by: Rosen Penev --- drivers/ata/sata_dwc_460ex.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/drivers/ata/sata_dwc_460ex.c b/drivers/ata/sata_dwc_460ex.c index bc543a408963..8e3fc713891a 100644 --- a/drivers/ata/sata_dwc_460ex.c +++ b/drivers/ata/sata_dwc_460ex.c @@ -607,14 +607,9 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance) status = ap->ops->sff_check_status(ap); dev_dbg(ap->dev, "%s ATA status register=0x%x\n", __func__, status); - tag = 0; while (tag_mask) { - while (!(tag_mask & 0x00000001)) { - tag++; - tag_mask <<= 1; - } - - tag_mask &= (~0x00000001); + tag = __ffs(tag_mask); + tag_mask &= ~(1U << tag); qc = ata_qc_from_tag(ap, tag); if (unlikely(!qc)) { dev_err(ap->dev, "failed to get qc"); -- 2.55.0