[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20190124190204.015211499@linuxfoundation.org>
Date: Thu, 24 Jan 2019 20:20:08 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Anders Roxell <anders.roxell@...aro.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 079/104] writeback: dont decrement wb->refcnt if !wb->bdi
4.4-stable review patch. If anyone has any objections, please let me know.
------------------
[ 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@...db.de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
include/linux/backing-dev-defs.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index a307c37c2e6c..072501a0ac86 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -225,6 +225,14 @@ static inline void wb_get(struct bdi_writeback *wb)
*/
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);
}
--
2.19.1
Powered by blists - more mailing lists