[kvm-unit-tests PATCH v5 0/2] Fixing infinite loop on SCLP READ SCP INFO error

[kvm-unit-tests PATCH v5 0/2] Fixing infinite loop on SCLP READ SCP INFO error

[Pierre Morel]

Aborting on SCLP READ SCP INFO error leads to a deadloop.

The loop is:
abort() -> exit() -> smp_teardown() -> smp_query_num_cpus() ->
sclp_get_cpu_num() -> assert() -> abort()

Since smp_setup() is done after sclp_read_info() inside setup() this
loop only happens when only the start processor is running.
Let sclp_get_cpu_num() return 1 in this case.

Also provide a bigger buffer for SCLP READ INFO when we have the
extended-length-SCCB facility.

Pierre

Pierre Morel (2):
  s390x: sclp: treat system as single processor when read_info is NULL
  s390x: sclp: Implement extended-length-SCCB facility

 lib/s390x/sclp.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

-- 
2.31.1

since v4:

- changed comments
  (Nico)

- use a big buffer from the start if possible
  (Claudio)

since v3:

- added initial patch and merge with comments
  Sorry for the noise.

since v2:

- use tabs in first patch
  (Nico)

- Added comments

- Added SCLP_RC_INSUFFICIENT_SCCB_LENGTH handling

[kvm-unit-tests PATCH v5 1/2] s390x: sclp: treat system as single processor when read_info is NULL

[Pierre Morel]

When a test abort()s before SCLP read info is completed, the assertion
on read_info in sclp_read_info() will fail. Since abort() eventually
calls smp_teardown() which in turn calls sclp_get_cpu_num(), this will
cause an infinite abort() chain, causing the test to hang.

Fix this by considering the system single processor when read_info is
missing.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
---
 lib/s390x/sclp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index acdc8a9..adf357b 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -119,8 +119,15 @@ void sclp_read_info(void)
 
 int sclp_get_cpu_num(void)
 {
-	assert(read_info);
-	return read_info->entries_cpu;
+	if (read_info)
+		return read_info->entries_cpu;
+	/*
+	 * Don't abort here if read_info is NULL since abort() calls
+	 * smp_teardown() which eventually calls this function and thus
+	 * causes an infinite abort() chain, causing the test to hang.
+	 * Since we obviously have at least one CPU, just return one.
+	 */
+	return 1;
 }
 
 CPUEntry *sclp_get_cpu_entries(void)
-- 
2.31.1

[kvm-unit-tests PATCH v5 2/2] s390x: sclp: Implement extended-length-SCCB facility

[Pierre Morel]

When the extended-length-SCCB facility is present use a big
buffer already at first try when calling sclp_read_scp_info()
to avoid the SCLP_RC_INSUFFICIENT_SCCB_LENGTH error.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
 lib/s390x/sclp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index adf357b..e44d299 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -17,13 +17,14 @@
 #include "sclp.h"
 #include <alloc_phys.h>
 #include <alloc_page.h>
+#include <asm/facility.h>
 
 extern unsigned long stacktop;
 
 static uint64_t storage_increment_size;
 static uint64_t max_ram_size;
 static uint64_t ram_size;
-char _read_info[PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
+char _read_info[2 * PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
 static ReadInfo *read_info;
 struct sclp_facilities sclp_facilities;
 
@@ -114,6 +115,8 @@ static void sclp_read_scp_info(ReadInfo *ri, int length)
 void sclp_read_info(void)
 {
 	sclp_read_scp_info((void *)_read_info, SCCB_SIZE);
+	sclp_read_scp_info((void *)_read_info,
+		test_facility(140) ? sizeof(_read_info) : SCCB_SIZE);
 	read_info = (ReadInfo *)_read_info;
 }
 
-- 
2.31.1

Re: [kvm-unit-tests PATCH v5 2/2] s390x: sclp: Implement extended-length-SCCB facility

[Pierre Morel]

On 6/1/23 18:45, Pierre Morel wrote:
> When the extended-length-SCCB facility is present use a big
> buffer already at first try when calling sclp_read_scp_info()
> to avoid the SCLP_RC_INSUFFICIENT_SCCB_LENGTH error.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>   lib/s390x/sclp.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
> index adf357b..e44d299 100644
> --- a/lib/s390x/sclp.c
> +++ b/lib/s390x/sclp.c
> @@ -17,13 +17,14 @@
>   #include "sclp.h"
>   #include <alloc_phys.h>
>   #include <alloc_page.h>
> +#include <asm/facility.h>
>   
>   extern unsigned long stacktop;
>   
>   static uint64_t storage_increment_size;
>   static uint64_t max_ram_size;
>   static uint64_t ram_size;
> -char _read_info[PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
> +char _read_info[2 * PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
>   static ReadInfo *read_info;
>   struct sclp_facilities sclp_facilities;
>   
> @@ -114,6 +115,8 @@ static void sclp_read_scp_info(ReadInfo *ri, int length)
>   void sclp_read_info(void)
>   {
This line must go away.....v
>   	sclp_read_scp_info((void *)_read_info, SCCB_SIZE);

Sorry for the noise.


> +	sclp_read_scp_info((void *)_read_info,
> +		test_facility(140) ? sizeof(_read_info) : SCCB_SIZE);
>   	read_info = (ReadInfo *)_read_info;
>   }
>   

Re: [kvm-unit-tests PATCH v5 0/2] Fixing infinite loop on SCLP READ SCP INFO error

[Nico Boehr]

Quoting Pierre Morel (2023-06-01 18:45:35)
> Aborting on SCLP READ SCP INFO error leads to a deadloop.
> 
> The loop is:
> abort() -> exit() -> smp_teardown() -> smp_query_num_cpus() ->
> sclp_get_cpu_num() -> assert() -> abort()
> 
> Since smp_setup() is done after sclp_read_info() inside setup() this
> loop only happens when only the start processor is running.
> Let sclp_get_cpu_num() return 1 in this case.
> 
> Also provide a bigger buffer for SCLP READ INFO when we have the
> extended-length-SCCB facility.
> 
> Pierre

Thanks for your patience Pierre.

Pushed to devel with the fixup to patch 2.