tpm: Provide strong locking for device removal
Add a read/write semaphore around the ops function pointers so
ops can be set to null when the driver un-registers.
Previously the tpm core expected module locking to be enough to
ensure that tpm_unregister could not be called during certain times,
however that hasn't been sufficient for a long time.
Introduce a read/write semaphore around 'ops' so the core can set
it to null when unregistering. This provides a strong fence around
the driver callbacks, guaranteeing to the driver that no callbacks
are running or will run again.
For now the ops_lock is placed very high in the call stack, it could
be pushed down and made more granular in future if necessary.
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
index d93736a..34e7fc7 100644
--- a/drivers/char/tpm/tpm-sysfs.c
+++ b/drivers/char/tpm/tpm-sysfs.c
@@ -295,5 +295,10 @@
void tpm_sysfs_del_device(struct tpm_chip *chip)
{
+ /* The sysfs routines rely on an implicit tpm_try_get_ops, this
+ * function is called before ops is null'd and the sysfs core
+ * synchronizes this removal so that no callbacks are running or can
+ * run again
+ */
sysfs_remove_group(&chip->dev.parent->kobj, &tpm_dev_group);
}