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Date: Fri, 22 Nov 2013 08:43:55 -0700 From: Bjorn Helgaas <bhelgaas@...gle.com> To: Tejun Heo <tj@...nel.org> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, "James E.J. Bottomley" <JBottomley@...allels.com> Subject: Re: [PATCH] sysfs: handle duplicate removal attempts in sysfs_remove_group() [+cc Rafael, James] On Tue, Nov 19, 2013 at 11:18 PM, Tejun Heo <tj@...nel.org> wrote: > (cc'ing Bjorn) > > Hello, > > On Tue, Nov 19, 2013 at 03:09:58PM +0200, Mika Westerberg wrote: >> Commit bcdde7e221a8 (sysfs: make __sysfs_remove_dir() recursive) changed >> the behavior so that directory removals will be done recursively. This >> means that the sysfs group might already be removed if its parent directory >> has been removed. >> >> The current code outputs warnings similar to following log snippet when it >> detects that there is no group for the given kobject: >> >> WARNING: CPU: 0 PID: 4 at fs/sysfs/group.c:214 sysfs_remove_group+0xc6/0xd0() >> sysfs group ffffffff81c6f1e0 not found for kobject 'host7' >> Modules linked in: >> CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted 3.12.0+ #13 >> Hardware name: /D33217CK, BIOS GKPPT10H.86A.0042.2013.0422.1439 04/22/2013 >> Workqueue: kacpi_hotplug acpi_hotplug_work_fn >> 0000000000000009 ffff8801002459b0 ffffffff817daab1 ffff8801002459f8 >> ffff8801002459e8 ffffffff810436b8 0000000000000000 ffffffff81c6f1e0 >> ffff88006d440358 ffff88006d440188 ffff88006e8b4c28 ffff880100245a48 >> Call Trace: >> [<ffffffff817daab1>] dump_stack+0x45/0x56 >> [<ffffffff810436b8>] warn_slowpath_common+0x78/0xa0 >> [<ffffffff81043727>] warn_slowpath_fmt+0x47/0x50 >> [<ffffffff811ae526>] sysfs_remove_group+0xc6/0xd0 >> [<ffffffff81432f7e>] dpm_sysfs_remove+0x3e/0x50 >> [<ffffffff8142a0d0>] device_del+0x40/0x1b0 >> [<ffffffff8142a24d>] device_unregister+0xd/0x20 >> [<ffffffff8144131a>] scsi_remove_host+0xba/0x110 >> [<ffffffff8145f526>] ata_host_detach+0xc6/0x100 >> [<ffffffff8145f578>] ata_pci_remove_one+0x18/0x20 >> [<ffffffff812e8f48>] pci_device_remove+0x28/0x60 >> [<ffffffff8142d854>] __device_release_driver+0x64/0xd0 >> [<ffffffff8142d8de>] device_release_driver+0x1e/0x30 >> [<ffffffff8142d257>] bus_remove_device+0xf7/0x140 >> [<ffffffff8142a1b1>] device_del+0x121/0x1b0 >> [<ffffffff812e43d4>] pci_stop_bus_device+0x94/0xa0 >> [<ffffffff812e437b>] pci_stop_bus_device+0x3b/0xa0 >> [<ffffffff812e437b>] pci_stop_bus_device+0x3b/0xa0 >> [<ffffffff812e44dd>] pci_stop_and_remove_bus_device+0xd/0x20 >> [<ffffffff812fc743>] trim_stale_devices+0x73/0xe0 >> [<ffffffff812fc78b>] trim_stale_devices+0xbb/0xe0 >> [<ffffffff812fc78b>] trim_stale_devices+0xbb/0xe0 >> [<ffffffff812fcb6e>] acpiphp_check_bridge+0x7e/0xd0 >> [<ffffffff812fd90d>] hotplug_event+0xcd/0x160 >> [<ffffffff812fd9c5>] hotplug_event_work+0x25/0x60 >> [<ffffffff81316749>] acpi_hotplug_work_fn+0x17/0x22 >> [<ffffffff8105cf3a>] process_one_work+0x17a/0x430 >> [<ffffffff8105db29>] worker_thread+0x119/0x390 >> [<ffffffff81063a5d>] kthread+0xcd/0xf0 >> [<ffffffff817eb33c>] ret_from_fork+0x7c/0xb0 > > So, we do have cases where the parent is removed before the child. I > suppose the parent pci bridge is removed already? AFAICS this > shouldn't break anything but people did seem to expect the removals to > be ordered from child to parent. Bjorn, is this something you expect > to happened? I do not expect a PCI bridge to be removed before the devices below it. We should be removing all the children before removing the parent bridge. But is this related to PCI? I don't see the connection yet. I tried to look into this a bit (my notes are at https://bugzilla.kernel.org/show_bug.cgi?id=65281), but I haven't figured out the big-picture problem yet. I don't have warm fuzzies that adding a "have we already removed this" check is the best resolution, but maybe that's just because I don't understand the problem. Bjorn >> I'm not 100% sure that this is the correct solution. It seem to fix my case >> but I might be missing something as I'm not that familiar with sysfs. > > Yeah, looks okay to me for now. One nit at the end tho. > > I find requiring removal of each sysfs attribute when the whole node > is going away rather weird. It forced us to have extra code which > does whole bunch of hash table lookups and deletion operations and the > only thing that achieved was either triggering warning if somebody did > it in the wrong order or spuriously, or leaking memory if somebody > forgot some without any way to find out about them. > > Now, all those are harmlessly unnecessary and we're adding more logic > to suppress warnings on specific cases. In the longer term, we > probably just wanna drop all the unnecessary removal logics and > warnings. > >> + /* >> + * Sysfs directories are now removed recursively by >> + * sysfs_remove_dir(). This means that this function can be called >> + * multiple times on the same group. If the parent directory is >> + * already removed we don't do anything here. >> + */ > > The function won't be called multiple times but may be called on a > group whose kobj whose sysfs entry is already removed in which case > all its groups are guaranteed to be already removed. > > Can you please update the comment to reflect the above? > > With that, > > Acked-by: Tejun Heo <tj@...nel.org> > > Thanks. > > -- > tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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