[PATCH 5.15 610/917] scsi: megaraid_sas: Fix concurrent access to ISR between IRQ polling and real interrupt

[Greg Kroah-Hartman]

From: Sumit Saxena <sumit.saxena@xxxxxxxxxxxx>

[ Upstream commit e7dcc514a49e74051b869697d5ab0370f6301d57 ]

IRQ polling thread calls ISR after enable_irq() to handle any missed I/O
completion. The atomic flag "in_used" was added to have the synchronization
between the IRQ polling thread and the interrupt context. There is a bug
around it leading to a race condition.

Below is the sequence:

 - IRQ polling thread accesses ISR, fetches the reply descriptor.

 - Real interrupt arrives and pre-empts polling thread (enable_irq() is
   already called).

 - Interrupt context picks the same reply descriptor as fetched by polling
   thread, processes it, and exits.

 - Polling thread resumes and processes the descriptor which is already
   processed by interrupt thread leads to kernel crash.

Setting the "in_used" flag before fetching the reply descriptor ensures
synchronized access to ISR.

Link: https://www.spinics.net/lists/linux-scsi/msg159440.html
Link: https://lore.kernel.org/r/20210929124022.24605-2-sumit.saxena@xxxxxxxxxxxx
Fixes: 9bedd36e9146 ("scsi: megaraid_sas: Handle missing interrupts while re-enabling IRQs")
Signed-off-by: Sumit Saxena <sumit.saxena@xxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/scsi/megaraid/megaraid_sas_fusion.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.c b/drivers/scsi/megaraid/megaraid_sas_fusion.c
index 26d0cf9353dd6..eb5ceb75a15ec 100644
--- a/drivers/scsi/megaraid/megaraid_sas_fusion.c
+++ b/drivers/scsi/megaraid/megaraid_sas_fusion.c
@@ -3530,6 +3530,9 @@ complete_cmd_fusion(struct megasas_instance *instance, u32 MSIxIndex,
 	if (atomic_read(&instance->adprecovery) == MEGASAS_HW_CRITICAL_ERROR)
 		return IRQ_HANDLED;
 
+	if (irq_context && !atomic_add_unless(&irq_context->in_used, 1, 1))
+		return 0;
+
 	desc = fusion->reply_frames_desc[MSIxIndex] +
 				fusion->last_reply_idx[MSIxIndex];
 
@@ -3540,11 +3543,11 @@ complete_cmd_fusion(struct megasas_instance *instance, u32 MSIxIndex,
 	reply_descript_type = reply_desc->ReplyFlags &
 		MPI2_RPY_DESCRIPT_FLAGS_TYPE_MASK;
 
-	if (reply_descript_type == MPI2_RPY_DESCRIPT_FLAGS_UNUSED)
+	if (reply_descript_type == MPI2_RPY_DESCRIPT_FLAGS_UNUSED) {
+		if (irq_context)
+			atomic_dec(&irq_context->in_used);
 		return IRQ_NONE;
-
-	if (irq_context && !atomic_add_unless(&irq_context->in_used, 1, 1))
-		return 0;
+	}
 
 	num_completed = 0;
 
-- 
2.33.0