s390/cpum_sf: Handle CPU hotplug remove during sampling

From: Thomas Richter <[email protected]>

[ Upstream commit a0bd7dacbd51c632b8e2c0500b479af564afadf3 ]

CPU hotplug remove handling triggers the following function call sequence:

CPUHP_AP_PERF_S390_SF_ONLINE --> s390_pmu_sf_offline_cpu()
...
CPUHP_AP_PERF_ONLINE --> perf_event_exit_cpu()

The s390 CPUMF sampling CPU hotplug handler invokes:

s390_pmu_sf_offline_cpu()

 +-->  cpusf_pmu_setup()
       +--> setup_pmc_cpu()
            +--> deallocate_buffers()

This function de-allocates all sampling data buffers (SDBs) allocated for that CPU at event initialization. It also clears the PMU_F_RESERVED bit. The CPU is gone and can not be sampled.

With the event still being active on the removed CPU, the CPU event hotplug support in kernel performance subsystem triggers the following function calls on the removed CPU:

perf_event_exit_cpu()

  +--> perf_event_exit_cpu_context()
       +--> __perf_event_exit_context()
	    +--> __perf_remove_from_context()
	         +--> event_sched_out()
	              +--> cpumsf_pmu_del()
	                   +--> cpumsf_pmu_stop()
                                +--> hw_perf_event_update()

to stop and remove the event. During removal of the event, the sampling device driver tries to read out the remaining samples from the sample data buffers (SDBs). But they have already been freed (and may have been re-assigned). This may lead to a use after free situation in which case the samples are most likely invalid. In the best case the memory has not been reassigned and still contains valid data.

Remedy this situation and check if the CPU is still in reserved state (bit PMU_F_RESERVED set). In this case the SDBs have not been released an contain valid data. This is always the case when the event is removed (and no CPU hotplug off occured). If the PMU_F_RESERVED bit is not set, the SDB buffers are gone.

---
 arch/s390/kernel/perf_cpum_sf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index c7f94b5d93968..e51babd0bbc10 100644
@@ -1772,7 +1772,9 @@ static void cpumsf_pmu_stop(struct perf_event *event, int flags)
 	event->hw.state |= PERF_HES_STOPPED;
 
 	if ((flags & PERF_EF_UPDATE) && !(event->hw.state & PERF_HES_UPTODATE)) {
-		hw_perf_event_update(event, 1);
+		/* CPU hotplug off removes SDBs. No samples to extract. */
+		if (cpuhw->flags & PMU_F_RESERVED)
+			hw_perf_event_update(event, 1);
 		event->hw.state |= PERF_HES_UPTODATE;
 	}
 	perf_pmu_enable(event->pmu);

2.43.0

From: Filipe Manana <[email protected]>

[ Upstream commit 2342d6595b608eec94187a17dc112dd4c2a812fa ]

Smatch complains about calling PTR_ERR() against a NULL pointer:

fs/btrfs/super.c:2272 btrfs_control_ioctl() warn: passing zero to 'PTR_ERR'

Fix this by calling PTR_ERR() against the device pointer only if it contains an error.

---
 fs/btrfs/super.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

index a595439518519..086d6d397f0be 100644
@@ -2283,7 +2283,10 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 					       &btrfs_root_fs_type);
 		if (IS_ERR(device)) {
 			mutex_unlock(&uuid_mutex);
-			ret = PTR_ERR(device);
+			if (IS_ERR(device))
+				ret = PTR_ERR(device);
+			else
+				ret = 0;
 			break;
 		}
 		ret = !(device->fs_devices->num_devices ==

2.43.0

Hi!

This patch was wrongly ported to 4.19. It is not needed there. Same test is already performed 2 lines above.

Please drop.

BR,
Pavel

DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany