Re: [PATCH v3 06/10] ACPI: extlog: Defer CXL protocol error handling to avoid lock inversion

[Shuai Xue <xueshuai@linux.alibaba.com>]

On 7/18/26 12:16 AM, Dave Jiang wrote:
> sashiko-bot flagged an AB-BA deadlock between the PCI device_lock and
> the MCE decoder chain rwsem.
> 
> extlog_print() calls cxl_cper_handle_prot_err() synchronously while the
> MCE notifier chain rwsem is held, and that path takes the PCI device_lock
> via guard(device)(). The probe path takes the locks in the opposite
> order (device_lock held while mce_register_decode_chain() takes the
> rwsem), so the two form an AB-BA deadlock.
> 
> ghes.c already avoids this by posting protocol errors to a kfifo and
> handling them from a workqueue via cxl_cper_post_prot_err(). Export that
> function and use it from acpi_extlog.c instead of calling
> cxl_cper_handle_prot_err() directly.
> 
> Reported-by: sashiko-bot@kernel.org
> Link: https://lore.kernel.org/linux-cxl/20260709165457.8BA181F000E9@smtp.kernel.org/
> Assisted-by: Claude:claude-sonnet-4-6
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
>   drivers/acpi/acpi_extlog.c | 23 +++--------------------
>   drivers/acpi/apei/ghes.c   |  5 +++--
>   include/acpi/ghes.h        |  4 ++++
>   3 files changed, 10 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
> index 0c440d75d9a7..ae79d090de33 100644
> --- a/drivers/acpi/acpi_extlog.c
> +++ b/drivers/acpi/acpi_extlog.c
> @@ -172,23 +172,6 @@ static void extlog_print_pcie(struct cper_sec_pcie *pcie_err,
>   #endif
>   }
>   
> -static void
> -extlog_cxl_cper_handle_prot_err(struct cxl_cper_sec_prot_err *prot_err,
> -				int severity, u32 len)
> -{
> -#ifdef ACPI_APEI_PCIEAER
> -	struct cxl_cper_prot_err_work_data wd;
> -
> -	if (cxl_cper_sec_prot_err_valid(prot_err, len))
> -		return;
> -
> -	if (cxl_cper_setup_prot_err_work_data(&wd, prot_err, severity))
> -		return;
> -
> -	cxl_cper_handle_prot_err(&wd);
> -#endif
> -}
> -
>   static int extlog_print(struct notifier_block *nb, unsigned long val,
>   			void *data)
>   {
> @@ -244,9 +227,9 @@ static int extlog_print(struct notifier_block *nb, unsigned long val,
>   			struct cxl_cper_sec_prot_err *prot_err =
>   				acpi_hest_get_payload(gdata);
>   
> -			extlog_cxl_cper_handle_prot_err(prot_err,
> -							gdata->error_severity,
> -							gdata->error_data_length);
> +			cxl_cper_post_prot_err(prot_err,
> +					       gdata->error_severity,
> +					       gdata->error_data_length);
>   		} else if (guid_equal(sec_type, &CPER_SEC_PCIE)) {
>   			struct cper_sec_pcie *pcie_err = acpi_hest_get_payload(gdata);
>   
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 17e4ef555292..b8dbd99da47e 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -752,8 +752,8 @@ static DEFINE_KFIFO(cxl_cper_prot_err_fifo, struct cxl_cper_prot_err_work_data,
>   static DEFINE_SPINLOCK(cxl_cper_prot_err_work_lock);
>   struct work_struct *cxl_cper_prot_err_work;
>   
> -static void cxl_cper_post_prot_err(struct cxl_cper_sec_prot_err *prot_err,
> -				   int severity, u32 len)
> +void cxl_cper_post_prot_err(struct cxl_cper_sec_prot_err *prot_err,
> +			    int severity, u32 len)
>   {
>   #ifdef CONFIG_ACPI_APEI_PCIEAER
>   	struct cxl_cper_prot_err_work_data wd;
> @@ -777,6 +777,7 @@ static void cxl_cper_post_prot_err(struct cxl_cper_sec_prot_err *prot_err,
>   	schedule_work(cxl_cper_prot_err_work);
>   #endif
>   }
> +EXPORT_SYMBOL_FOR_MODULES(cxl_cper_post_prot_err, "acpi_extlog");
>   
>   int cxl_cper_register_prot_err_work(struct work_struct *work)
>   {
> diff --git a/include/acpi/ghes.h b/include/acpi/ghes.h
> index 8d7e5caef3f1..4dcbb2c30ea2 100644
> --- a/include/acpi/ghes.h
> +++ b/include/acpi/ghes.h
> @@ -143,4 +143,8 @@ static inline int ghes_notify_sea(void) { return -ENOENT; }
>   struct notifier_block;
>   extern void ghes_register_report_chain(struct notifier_block *nb);
>   extern void ghes_unregister_report_chain(struct notifier_block *nb);
> +
> +struct cxl_cper_sec_prot_err;
> +void cxl_cper_post_prot_err(struct cxl_cper_sec_prot_err *prot_err,
> +			    int severity, u32 len);
>   #endif /* GHES_H */

The declaration lands outside the CONFIG_ACPI_APEI_GHES section,
but the definition only exists in ghes.c, which is not built when
ACPI_APEI_GHES is disabled. ACPI_EXTLOG doesn't depend on GHES, so
GHES=n + EXTLOG=m is a legal config and modpost will fail on the
missing symbol. Either move the declaration into the GHES block with
a stub in the #else, or add the Kconfig dependency.

Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>

Thanks.
Shuai