[ Upstream commit
347a28b586802d09604a149c1a1f6de5dccbe6fa ]
This happened while running in qemu-system-aarch64, the AMBA PL011 UART
driver when enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE.
arch_initcall(pl011_init) came before subsys_initcall(default_bdi_init),
devtmpfs' handle_remove() crashes because the reference count is a NULL
pointer only because wb->bdi hasn't been initialized yet.
Rework so that wb_put have an extra check if wb->bdi before decrement
wb->refcnt and also add a WARN_ON_ONCE to get a warning if it happens again
in other drivers.
Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
*/
static inline void wb_put(struct bdi_writeback *wb)
{
+ if (WARN_ON_ONCE(!wb->bdi)) {
+ /*
+ * A driver bug might cause a file to be removed before bdi was
+ * initialized.
+ */
+ return;
+ }
+
if (wb != &wb->bdi->wb)
percpu_ref_put(&wb->refcnt);
}