2020-02-23 16:57:11

by Amol Grover

Subject: [PATCH RESEND] iommu: dmar: Fix RCU list debugging warnings

dmar_drhd_units is traversed using list_for_each_entry_rcu()
outside of an RCU read side critical section but under the
protection of dmar_global_lock. Hence add corresponding lockdep
expression to silence the following false-positive warnings:

[ 1.603975] =============================
[ 1.603976] WARNING: suspicious RCU usage
[ 1.603977] 5.5.4-stable #17 Not tainted
[ 1.603978] -----------------------------
[ 1.603980] drivers/iommu/intel-iommu.c:4769 RCU-list traversed in non-reader section!!

[ 1.603869] =============================
[ 1.603870] WARNING: suspicious RCU usage
[ 1.603872] 5.5.4-stable #17 Not tainted
[ 1.603874] -----------------------------
[ 1.603875] drivers/iommu/dmar.c:293 RCU-list traversed in non-reader section!!

Tested-by: Madhuparna Bhowmik <[email protected]>
Signed-off-by: Amol Grover <[email protected]>
---
include/linux/dmar.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index f64ca27dc210..712be8bc6a7c 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -69,8 +69,9 @@ struct dmar_pci_notify_info {
extern struct rw_semaphore dmar_global_lock;
extern struct list_head dmar_drhd_units;

-#define for_each_drhd_unit(drhd) \
- list_for_each_entry_rcu(drhd, &dmar_drhd_units, list)
+#define for_each_drhd_unit(drhd) \
+ list_for_each_entry_rcu(drhd, &dmar_drhd_units, list, \
+ dmar_rcu_check())

#define for_each_active_drhd_unit(drhd) \
list_for_each_entry_rcu(drhd, &dmar_drhd_units, list) \
@@ -81,7 +82,8 @@ extern struct list_head dmar_drhd_units;
if (i=drhd->iommu, drhd->ignored) {} else

#define for_each_iommu(i, drhd) \
- list_for_each_entry_rcu(drhd, &dmar_drhd_units, list) \
+ list_for_each_entry_rcu(drhd, &dmar_drhd_units, list, \
+ dmar_rcu_check()) \
if (i=drhd->iommu, 0) {} else

static inline bool dmar_rcu_check(void)
--
2.24.1

2020-02-23 23:38:38

by Lu Baolu

Subject: Re: [PATCH RESEND] iommu: dmar: Fix RCU list debugging warnings

On 2020/2/24 0:55, Amol Grover wrote:
> dmar_drhd_units is traversed using list_for_each_entry_rcu()
> outside of an RCU read side critical section but under the
> protection of dmar_global_lock. Hence add corresponding lockdep
> expression to silence the following false-positive warnings:
>
> [ 1.603975] =============================
> [ 1.603976] WARNING: suspicious RCU usage
> [ 1.603977] 5.5.4-stable #17 Not tainted
> [ 1.603978] -----------------------------
> [ 1.603980] drivers/iommu/intel-iommu.c:4769 RCU-list traversed in non-reader section!!
>
> [ 1.603869] =============================
> [ 1.603870] WARNING: suspicious RCU usage
> [ 1.603872] 5.5.4-stable #17 Not tainted
> [ 1.603874] -----------------------------
> [ 1.603875] drivers/iommu/dmar.c:293 RCU-list traversed in non-reader section!!
>
> Tested-by: Madhuparna Bhowmik <[email protected]>
> Signed-off-by: Amol Grover <[email protected]>

Thanks for the fix.

Cc: [email protected]
Acked-by: Lu Baolu <[email protected]>

Best regards,
baolu

2020-03-02 16:04:47

by Joerg Roedel

Subject: Re: [PATCH RESEND] iommu: dmar: Fix RCU list debugging warnings

On Sun, Feb 23, 2020 at 10:25:39PM +0530, Amol Grover wrote:
> dmar_drhd_units is traversed using list_for_each_entry_rcu()
> outside of an RCU read side critical section but under the
> protection of dmar_global_lock. Hence add corresponding lockdep
> expression to silence the following false-positive warnings:
>
> [ 1.603975] =============================
> [ 1.603976] WARNING: suspicious RCU usage
> [ 1.603977] 5.5.4-stable #17 Not tainted
> [ 1.603978] -----------------------------
> [ 1.603980] drivers/iommu/intel-iommu.c:4769 RCU-list traversed in non-reader section!!
>
> [ 1.603869] =============================
> [ 1.603870] WARNING: suspicious RCU usage
> [ 1.603872] 5.5.4-stable #17 Not tainted
> [ 1.603874] -----------------------------
> [ 1.603875] drivers/iommu/dmar.c:293 RCU-list traversed in non-reader section!!
>
> Tested-by: Madhuparna Bhowmik <[email protected]>
> Signed-off-by: Amol Grover <[email protected]>
> ---
> include/linux/dmar.h | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)

Applied, thanks.