On Tue, Jun 15 2021, Christoph Hellwig [off-list ref] wrote:

EPROBE_DEFER is an internal kernel error code and it should not be leaked
to userspace via the bind_store() sysfs. Userspace doesn't have this
constant and cannot understand it.

Further, it doesn't really make sense to have userspace trigger a deferred
probe via bind_store(), which could eventually succeed, while
simultaneously returning an error back.

Resolve this by splitting driver_probe_device so that the version used
by the sysfs binding that turns EPROBE_DEFER into -EAGAIN, while the one
used for internally binding keeps the error code, and calls
driver_deferred_probe_add where needed.  This also allows to nicely split
out the defer_all_probes / probe_count checks so that they actually allow
for full device_{block,unblock}_probing protection while not bothering
the sysfs bind case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/dd.c | 78 +++++++++++++++++++++++++----------------------
 1 file changed, 42 insertions(+), 36 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>