| Message ID | 20181017140311.28679-2-anders.roxell@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] serial: set suppress_bind_attrs flag only if builtin | expand |
On Wed, 17 Oct 2018 16:03:11 +0200 Anders Roxell <anders.roxell@linaro.org> wrote: > When enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE devtmpfs gets killed > because we try to remove a file and decrement the wb reference count > before the noop_backing_device_info gets initialized. > > Since 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 bdi->wb > hasn't been initialized yet. Is this changelog correct? What does drivers/tty/serial/amba-pl011.c have to do with page writeback? Confused. > [ 0.332075] Serial: AMBA PL011 UART driver > [ 0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1 > [ 0.502382] console [ttyAMA0] enabled > [ 0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000 > [ 0.516053] Mem abort info: > [ 0.516222] ESR = 0x96000004 > [ 0.516417] Exception class = DABT (current EL), IL = 32 bits > [ 0.516641] SET = 0, FnV = 0 > [ 0.516826] EA = 0, S1PTW = 0 > [ 0.516984] Data abort info: > [ 0.517149] ISV = 0, ISS = 0x00000004 > [ 0.517339] CM = 0, WnR = 0 > [ 0.517553] [0000800074c12000] user address but active_mm is swapper > [ 0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP > [ 0.518305] Modules linked in: > [ 0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82 > [ 0.519307] Hardware name: linux,dummy-virt (DT) > [ 0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO) > [ 0.519959] pc : __destroy_inode+0x94/0x2a8 > [ 0.520212] lr : __destroy_inode+0x78/0x2a8 > [ 0.520401] sp : ffff0000098c3b20 > [ 0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714 > [ 0.520904] x27: 0000000000002000 x26: 0000000000002000 > [ 0.521179] x25: ffff000009583000 x24: 0000000000000000 > [ 0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0 > [ 0.521737] x21: ffff0000093f9338 x20: 0000000000000000 > [ 0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400 > [ 0.522376] x17: 0000000000000000 x16: 0000000000000000 > [ 0.522727] x15: 0000000000000400 x14: 0000000000000400 > [ 0.523068] x13: 0000000000000001 x12: 0000000000000001 > [ 0.523421] x11: 0000000000000000 x10: 0000000000000970 > [ 0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190 > [ 0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88 > [ 0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb > [ 0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff > [ 0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000 > [ 0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____)) > [ 0.525529] Call trace: > [ 0.525806] __destroy_inode+0x94/0x2a8 > [ 0.526108] destroy_inode+0x34/0x88 > [ 0.526370] evict+0x144/0x1c8 > [ 0.526636] iput+0x184/0x230 > [ 0.526871] dentry_unlink_inode+0x118/0x130 > [ 0.527152] d_delete+0xd8/0xe0 > [ 0.527420] vfs_unlink+0x240/0x270 > [ 0.527665] handle_remove+0x1d8/0x330 > [ 0.527875] devtmpfsd+0x138/0x1c8 > [ 0.528085] kthread+0x14c/0x158 > [ 0.528291] ret_from_fork+0x10/0x18 > [ 0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04) Seems that there is indeed some form of linkage. Can this be spelled out more in the changelog please? > > Rework so that wb_put have an extra check if wb->bdi before decrement > wb->refcnt and also add a WARN_ON to get a warning if it happens again > in other drivers. > > Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") > Cc: Arnd Bergmann <arnd@arndb.de> > Co-developed-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> Signed-off-by: Arnd, please. > --- a/include/linux/backing-dev-defs.h > +++ b/include/linux/backing-dev-defs.h > @@ -258,7 +258,7 @@ static inline void wb_get(struct bdi_writeback *wb) > */ > static inline void wb_put(struct bdi_writeback *wb) > { > - if (wb != &wb->bdi->wb) > + if (!WARN_ON(!wb->bdi) && wb != &wb->bdi->wb) > percpu_ref_put(&wb->refcnt); > } The !WARN_ON(!expr) isn't very easy to follow. This: { if (WARN_ON_ONCE(!wb->bdi)) { /* * Nice comment explaining how this situation comes about */ return; } if (wb != &wb->bdi->wb) percpu_ref_put(&wb->refcnt); } is better, no? Also, please note the s/WARN_ON/WARN_ON_ONCE/. I don't think we gain anything from reporting the same thing many times?
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 9a6bc0951cfa..20721550d32a 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -258,7 +258,7 @@ static inline void wb_get(struct bdi_writeback *wb) */ static inline void wb_put(struct bdi_writeback *wb) { - if (wb != &wb->bdi->wb) + if (!WARN_ON(!wb->bdi) && wb != &wb->bdi->wb) percpu_ref_put(&wb->refcnt); }
When enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE devtmpfs gets killed because we try to remove a file and decrement the wb reference count before the noop_backing_device_info gets initialized. Since 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 bdi->wb hasn't been initialized yet. [ 0.332075] Serial: AMBA PL011 UART driver [ 0.485276] 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 39, base_baud = 0) is a PL011 rev1 [ 0.502382] console [ttyAMA0] enabled [ 0.515710] Unable to handle kernel paging request at virtual address 0000800074c12000 [ 0.516053] Mem abort info: [ 0.516222] ESR = 0x96000004 [ 0.516417] Exception class = DABT (current EL), IL = 32 bits [ 0.516641] SET = 0, FnV = 0 [ 0.516826] EA = 0, S1PTW = 0 [ 0.516984] Data abort info: [ 0.517149] ISV = 0, ISS = 0x00000004 [ 0.517339] CM = 0, WnR = 0 [ 0.517553] [0000800074c12000] user address but active_mm is swapper [ 0.517928] Internal error: Oops: 96000004 [#1] PREEMPT SMP [ 0.518305] Modules linked in: [ 0.518839] CPU: 0 PID: 13 Comm: kdevtmpfs Not tainted 4.19.0-rc5-next-20180928-00002-g2ba39ab0cd01-dirty #82 [ 0.519307] Hardware name: linux,dummy-virt (DT) [ 0.519681] pstate: 80000005 (Nzcv daif -PAN -UAO) [ 0.519959] pc : __destroy_inode+0x94/0x2a8 [ 0.520212] lr : __destroy_inode+0x78/0x2a8 [ 0.520401] sp : ffff0000098c3b20 [ 0.520590] x29: ffff0000098c3b20 x28: 00000000087a3714 [ 0.520904] x27: 0000000000002000 x26: 0000000000002000 [ 0.521179] x25: ffff000009583000 x24: 0000000000000000 [ 0.521467] x23: ffff80007bb52000 x22: ffff80007bbaa7c0 [ 0.521737] x21: ffff0000093f9338 x20: 0000000000000000 [ 0.522033] x19: ffff80007bbb05d8 x18: 0000000000000400 [ 0.522376] x17: 0000000000000000 x16: 0000000000000000 [ 0.522727] x15: 0000000000000400 x14: 0000000000000400 [ 0.523068] x13: 0000000000000001 x12: 0000000000000001 [ 0.523421] x11: 0000000000000000 x10: 0000000000000970 [ 0.523749] x9 : ffff0000098c3a60 x8 : ffff80007bbab190 [ 0.524017] x7 : ffff80007bbaa880 x6 : 0000000000000c88 [ 0.524305] x5 : ffff0000093d96c8 x4 : 61c8864680b583eb [ 0.524567] x3 : ffff0000093d6180 x2 : ffffffffffffffff [ 0.524872] x1 : 0000800074c12000 x0 : 0000800074c12000 [ 0.525207] Process kdevtmpfs (pid: 13, stack limit = 0x(____ptrval____)) [ 0.525529] Call trace: [ 0.525806] __destroy_inode+0x94/0x2a8 [ 0.526108] destroy_inode+0x34/0x88 [ 0.526370] evict+0x144/0x1c8 [ 0.526636] iput+0x184/0x230 [ 0.526871] dentry_unlink_inode+0x118/0x130 [ 0.527152] d_delete+0xd8/0xe0 [ 0.527420] vfs_unlink+0x240/0x270 [ 0.527665] handle_remove+0x1d8/0x330 [ 0.527875] devtmpfsd+0x138/0x1c8 [ 0.528085] kthread+0x14c/0x158 [ 0.528291] ret_from_fork+0x10/0x18 [ 0.528720] Code: 92800002 aa1403e0 d538d081 8b010000 (c85f7c04) [ 0.529367] ---[ end trace 5a3dee47727f877c ]--- Rework so that wb_put have an extra check if wb->bdi before decrement wb->refcnt and also add a WARN_ON to get a warning if it happens again in other drivers. Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") Cc: Arnd Bergmann <arnd@arndb.de> Co-developed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- include/linux/backing-dev-defs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)