intel_th: Don't reference unassigned outputs

When an output port driver is removed, also remove references to it from
any masters. Failing to do this causes a NULL ptr dereference when
configuring another output port:

> BUG: unable to handle kernel NULL pointer dereference at 000000000000000d
> RIP: 0010:master_attr_store+0x9d/0x160 [intel_th_gth]
> Call Trace:
> dev_attr_store+0x1b/0x30
> sysfs_kf_write+0x3c/0x50
> kernfs_fop_write+0x125/0x1a0
> __vfs_write+0x3a/0x190
> ? __vfs_write+0x5/0x190
> ? _cond_resched+0x1a/0x50
> ? rcu_all_qs+0x5/0xb0
> ? __vfs_write+0x5/0x190
> vfs_write+0xb8/0x1b0
> ksys_write+0x55/0xc0
> __x64_sys_write+0x1a/0x20
> do_syscall_64+0x5a/0x140
> entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: b27a6a3f97b9 ("intel_th: Add Global Trace Hub driver")
CC: stable@vger.kernel.org # v4.4+
Reported-by: Ammy Yi <ammy.yi@intel.com>

diff --git a/drivers/hwtracing/intel_th/gth.c b/drivers/hwtracing/intel_th/gth.c
index 8426b79..cc287cf 100644 (file)
--- a/drivers/hwtracing/intel_th/gth.c
+++ b/drivers/hwtracing/intel_th/gth.c
@@ -607,6 +607,7 @@ static void intel_th_gth_unassign(struct intel_th_device *thdev,
 {
        struct gth_device *gth = dev_get_drvdata(&thdev->dev);
        int port = othdev->output.port;
+       int master;
 
        if (thdev->host_mode)
                return;
@@ -615,6 +616,9 @@ static void intel_th_gth_unassign(struct intel_th_device *thdev,
        othdev->output.port = -1;
        othdev->output.active = false;
        gth->output[port].output = NULL;
+       for (master = 0; master < TH_CONFIGURABLE_MASTERS; master++)
+               if (gth->master[master] == port)
+                       gth->master[master] = -1;
        spin_unlock(&gth->gth_lock);
 }