linux-kernel - [PATCH] ACPI: APEI: do not add task

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Message-Id: <20220916050535.26625-1-xueshuai@linux.alibaba.com>
Date:   Fri, 16 Sep 2022 13:05:35 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     rafael@...nel.org, lenb@...nel.org, james.morse@....com,
        tony.luck@...el.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        jarkko@...nel.org, naoya.horiguchi@....com, linmiaohe@...wei.com,
        akpm@...ux-foundation.org
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        cuibixuan@...ux.alibaba.com, baolin.wang@...ux.alibaba.com,
        zhuo.song@...ux.alibaba.com, xueshuai@...ux.alibaba.com
Subject: [PATCH] ACPI: APEI: do not add task_work for outside context error

If an error is detected as a result of user-space process accessing a
corrupt memory location, the CPU may take an abort. Then the platform
firmware reports kernel via NMI like notifications, e.g. NOTIFY_SEA,
NOTIFY_SOFTWARE_DELEGATED, etc.

For NMI like notifications, commit 7f17b4a121d0 ("ACPI: APEI: Kick the
memory_failure() queue for synchronous errors") keep track of whether
memory_failure() work was queued, and make task_work pending to flush out
the queue so that the work is processed before return to user-space.

The code use init_mm to check whether the error occurs in user space:

    if (current->mm != &init_mm)

The condition is always true, becase _nobody_ ever has "init_mm" as a real
VM any more and should generally just do

    if (current->mm)

as described in active_mm.rst documentation.

Then if an error is detected outside of the current execution context (e.g.
when detected by a background scrubber), do not add task_work as the
original patch intends to do.

Fixes: 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for synchronous errors")
Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
---
 drivers/acpi/apei/ghes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index d91ad378c00d..80ad530583c9 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -985,7 +985,7 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
 				ghes_estatus_cache_add(generic, estatus);
 		}

-		if (task_work_pending && current->mm != &init_mm) {
+		if (task_work_pending && current->mm) {
 			estatus_node->task_work.func = ghes_kick_task_work;
 			estatus_node->task_work_cpu = smp_processor_id();
 			ret = task_work_add(current, &estatus_node->task_work,
-- 
2.20.1.12.g72788fdb