Messages in this thread Patch in this message | | | From | Anders Roxell <> | Subject | [PATCH v2 2/2] writeback: don't decrement wb->refcnt if !wb->bdi | Date | Tue, 30 Oct 2018 12:35:45 +0100 |
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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> --- 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 9a6bc0951cfa..c31157135598 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -258,6 +258,14 @@ 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
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