At Wed, 30 Jul 2014 11:40:14 -0400, Josef Bacik wrote: > > On 07/30/2014 11:05 AM, Takashi Iwai wrote: > > At Wed, 30 Jul 2014 17:01:52 +0200, > > Takashi Iwai wrote: > >> > >> At Wed, 30 Jul 2014 10:29:46 -0400, > >> Josef Bacik wrote: > >>> > >>> On 07/30/2014 05:57 AM, Takashi Iwai wrote: > >>>> At Mon, 28 Jul 2014 16:01:55 +0200, > >>>> Takashi Iwai wrote: > >>>>> > >>>>> At Mon, 28 Jul 2014 15:48:41 +0200, > >>>>> Takashi Iwai wrote: > >>>>>> > >>>>>> At Mon, 28 Jul 2014 09:16:48 -0400, > >>>>>> Josef Bacik wrote: > >>>>>>> > >>>>>>> On 07/28/2014 04:57 AM, Takashi Iwai wrote: > >>>>>>>> We've got bug reports that btrfs crashes when quota is enabled on > >>>>>>>> 32bit kernel, typically with the Oops like below: > >>>>>>>> BUG: unable to handle kernel NULL pointer dereference at 00000004 > >>>>>>>> IP: [<f9234590>] find_parent_nodes+0x360/0x1380 [btrfs] > >>>>>>>> *pde = 00000000 > >>>>>>>> Oops: 0000 [#1] SMP > >>>>>>>> CPU: 0 PID: 151 Comm: kworker/u8:2 Tainted: G S W > >>>>>>>> 3.15.2-1.gd43d97e-default #1 > >>>>>>>> Workqueue: btrfs-qgroup-rescan normal_work_helper [btrfs] > >>>>>>>> task: f1478130 ti: f147c000 task.ti: f147c000 > >>>>>>>> EIP: 0060:[<f9234590>] EFLAGS: 00010213 CPU: 0 > >>>>>>>> EIP is at find_parent_nodes+0x360/0x1380 [btrfs] > >>>>>>>> EAX: f147dda8 EBX: f147ddb0 ECX: 00000011 EDX: 00000000 > >>>>>>>> ESI: 00000000 EDI: f147dda4 EBP: f147ddf8 ESP: f147dd38 > >>>>>>>> DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 > >>>>>>>> CR0: 8005003b CR2: 00000004 CR3: 00bf3000 CR4: 00000690 > >>>>>>>> Stack: > >>>>>>>> 00000000 00000000 f147dda4 00000050 00000001 00000000 00000001 > >>>>>>>> 00000050 > >>>>>>>> 00000001 00000000 d3059000 00000001 00000022 000000a8 00000000 > >>>>>>>> 00000000 > >>>>>>>> 00000000 000000a1 00000000 00000000 00000001 00000000 00000000 > >>>>>>>> 11800000 > >>>>>>>> Call Trace: > >>>>>>>> [<f923564d>] __btrfs_find_all_roots+0x9d/0xf0 [btrfs] > >>>>>>>> [<f9237bb1>] btrfs_qgroup_rescan_worker+0x401/0x760 [btrfs] > >>>>>>>> [<f9206148>] normal_work_helper+0xc8/0x270 [btrfs] > >>>>>>>> [<c025e38b>] process_one_work+0x11b/0x390 > >>>>>>>> [<c025eea1>] worker_thread+0x101/0x340 > >>>>>>>> [<c026432b>] kthread+0x9b/0xb0 > >>>>>>>> [<c0712a71>] ret_from_kernel_thread+0x21/0x30 > >>>>>>>> [<c0264290>] kthread_create_on_node+0x110/0x110 > >>>>>>>> > >>>>>>>> This indicates a NULL corruption in prefs_delayed list. The further > >>>>>>>> investigation and bisection pointed that the call of > >>>>>>>> ulist_add_merge() > >>>>>>>> results in the corruption. > >>>>>>>> > >>>>>>>> ulist_add_merge() takes u64 as aux and writes a 64bit value into > >>>>>>>> old_aux. The callers of this function in backref.c, however, pass a > >>>>>>>> pointer of a pointer to old_aux. That is, the function overwrites > >>>>>>>> 64bit value on 32bit pointer. This caused a NULL in the adjacent > >>>>>>>> variable, in this case, prefs_delayed. > >>>>>>>> > >>>>>>>> Here is a quick attempt to band-aid over this: a new function, > >>>>>>>> ulist_add_merge_ptr() is introduced to pass/store properly a pointer > >>>>>>>> value instead of u64. There are still ugly void ** cast remaining > >>>>>>>> in the callers because void ** cannot be taken implicitly. But, it's > >>>>>>>> safer than explicit cast to u64, anyway. > >>>>>>>> > >>>>>>>> Bugzilla: > >>>>>>>> https://urldefense.proofpoint.com/v1/url?u=https://bugzilla.novell.com/show_bug.cgi?id%3D887046&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKsMpTX8ybrSkonQ%3D%3D%0A&m=m3qrbo6ngjqKO%2B7ofuwRfQflb9Cx%2FXrF8TKejkPjxfA%3D%0A&s=199a5b6f0ed181925e9ba2c1060fe20d1c8ad2831dd1d96cc7eddd2a343fa72b > >>>>>>>> Cc: <sta...@vger.kernel.org> [v3.11+] > >>>>>>>> Signed-off-by: Takashi Iwai <ti...@suse.de> > >>>>>>>> --- > >>>>>>>> > >>>>>>>> Alternatively, we can change the argument of aux and old_aux to a > >>>>>>>> pointer from u64, as backref.c is the only user of ulist_add_merge() > >>>>>>>> function. I'll cook up another patch if it's the preferred way. > >>>>>>>> > >>>>>>> > >>>>>>> Yeah lets just use a pointer and see how that works out. Thanks, > >>>>>> > >>>>>> Oops, I forgot that ulist_add() takes aux as u64 and it calling > >>>>>> ulist_add_merge() internally. So, we can't change the type blindly > >>>>>> there, unfortunately. > >>>>> > >>>>> Looking back at the code, it seems that all aux arguments passed to > >>>>> ulist_add() in qgroup.c are pointers, too. So, indeed, all aux values > >>>>> are pointers, so far, and it'd be even cleaner to replace all these > >>>>> from u64 to void *. > >>>>> > >>>>> But, such a replacement patch will become difficult for backporting to > >>>>> stable kernels (the bug existed since 3.11, at least). So IMO, we > >>>>> should put a smaller fix like my previous one, let it backported to > >>>>> stable kernels, and do more comprehensive replacements to pointer on > >>>>> its top. > >>>> > >>>> Ping. Could you guys take my original patch as is, or do you prefer > >>>> changing in a different way? If so, how? > >>>> > >>> > >>> I don't care how hard it is to backport to stable, > >> > >> You must do care as a maintainer. It's a long-standing and serious > >> bug since 3.11. The kernel hangs up immediately when you enable quota > >> on 32bit kernel. And it's really hard to revert it when the rootfs is > >> btrfs. (The mount follows the immediate hang up after reboot.) > >> > > What I mean is that we want the right fix first, not something that is easier > to > pull back to stable and then the right fix later. Do it right first and then > backport it to the stable kernels, it's perfectly acceptable to adjust patches > when sending them to the stable team. "But it's hard" is not a valid excuse > for > not doing it right the first time.
Well, I guess this underestimates the burden of backports. Currently, there is stable kernel for each kernel release. Anyone has to backport for each version, and you'll be asked. I, as a long-time subsystem maintainer, wouldn't go in that way :) And, speaking of "rightness" -- replacing the callers with a wrapper is also a right fix. It's even a safer fix. That's basically why I posted it as the primary patch. The merit of replacing all callers is that you can eliminate nasty casts by that. This is however rather a cleanup, which is a different bonus from what we need to fix. > >>> since we're using pointers > >>> everywhere just change it to void * and be done with it. Thanks, > >> > >> Fix it quickly, then do cleanup. This is the golden rule for > >> regression :) > > > > Also, another question is whether you guys are OK to change the type > > to a pointer. Through a glance, the ulist code was intended to handle > > any generic data, thus it uses u64, right? Using void pointer breaks > > this concept. > > > > It's fine, ulist today resembles very little from what it was originally. The > current users all shove pointers into there, so we might as well just make it > a > pointer. Thanks, OK, good to know. If this post still doesn't convince you, I'll prepare the patch to do all replacements. thanks, Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
