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From:   Baochen Qiang <quic_bqiang@quicinc.com>
To:     <ath11k@lists.infradead.org>
CC:     <linux-wireless@vger.kernel.org>
Subject: [PATCH] wifi: ath11k: fix race due to setting ATH11K_FLAG_EXT_IRQ_ENABLED too early
Date:   Fri, 17 Nov 2023 08:39:19 +0800
Message-ID: <20231117003919.26218-1-quic_bqiang@quicinc.com>
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Precedence: bulk

We are seeing below error randomly in the case where only
one MSI vector is configured:

kernel: ath11k_pci 0000:03:00.0: wmi command 16387 timeout

The reason is, currently, in ath11k_pcic_ext_irq_enable(),
ATH11K_FLAG_EXT_IRQ_ENABLED is set before NAPI is enabled.
This results in a race condition: after
ATH11K_FLAG_EXT_IRQ_ENABLED is set but before NAPI enabled,
CE interrupt breaks in. Since IRQ is shared by CE and data
path, ath11k_pcic_ext_interrupt_handler() is also called
where we call disable_irq_nosync() to disable IRQ. Then
napi_schedule() is called but it does nothing because NAPI
is not enabled at that time, meaning
ath11k_pcic_ext_grp_napi_poll() will never run, so we have
no chance to call enable_irq() to enable IRQ back. Finally
we get above error.

Fix it by setting ATH11K_FLAG_EXT_IRQ_ENABLED after all
NAPI and IRQ work are done. With the fix, we are sure that
by the time ATH11K_FLAG_EXT_IRQ_ENABLED is set, NAPI is
enabled.

Note that the fix above also introduce some side effects:
if ath11k_pcic_ext_interrupt_handler() breaks in after NAPI
enabled but before ATH11K_FLAG_EXT_IRQ_ENABLED set, nothing
will be done by the handler this time, the work will be
postponed till the next time the IRQ fires.

Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.23

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
---
 drivers/net/wireless/ath/ath11k/pcic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/ath/ath11k/pcic.c b/drivers/net/wireless/ath/ath11k/pcic.c
index 16d1e332193f..e602d4130105 100644
--- a/drivers/net/wireless/ath/ath11k/pcic.c
+++ b/drivers/net/wireless/ath/ath11k/pcic.c
@@ -460,8 +460,6 @@ void ath11k_pcic_ext_irq_enable(struct ath11k_base *ab)
 {
 	int i;
 
-	set_bit(ATH11K_FLAG_EXT_IRQ_ENABLED, &ab->dev_flags);
-
 	for (i = 0; i < ATH11K_EXT_IRQ_GRP_NUM_MAX; i++) {
 		struct ath11k_ext_irq_grp *irq_grp = &ab->ext_irq_grp[i];
 
@@ -471,6 +469,8 @@ void ath11k_pcic_ext_irq_enable(struct ath11k_base *ab)
 		}
 		ath11k_pcic_ext_grp_enable(irq_grp);
 	}
+
+	set_bit(ATH11K_FLAG_EXT_IRQ_ENABLED, &ab->dev_flags);
 }
 EXPORT_SYMBOL(ath11k_pcic_ext_irq_enable);
 

base-commit: 9a36440d929d134c56030a8492405708a143f580
-- 
2.25.1