Messages in this thread Patch in this message | | | Subject | [RFC PATCH v3] Use kernfs_break_active_protection() for device online store callbacks | From | Li Zhong <> | Date | Mon, 14 Apr 2014 15:47:29 +0800 |
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I noticed following lockdep warning when trying acpi hot-remove cpus:
[84154.204080] ====================================================== [84154.204080] [ INFO: possible circular locking dependency detected ] [84154.204080] 3.14.0-next-20140408+ #24 Tainted: G W [84154.204080] ------------------------------------------------------- [84154.204080] bash/777 is trying to acquire lock: [84154.204080] (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff810664a7>] cpu_maps_update_begin+0x17/0x20 [84154.213203] [84154.213203] but task is already holding lock: [84154.213203] (s_active#79){++++.+}, at: [<ffffffff81256e14>] kernfs_fop_write+0xe4/0x190 [84154.213203] [84154.213203] which lock already depends on the new lock. [84154.213203] [84154.213203] [84154.213203] the existing dependency chain (in reverse order) is: [84154.213203] -> #3 (s_active#79){++++.+}: [84154.213203] [<ffffffff810c408b>] lock_acquire+0x9b/0x1d0 [84154.213203] [<ffffffff812552e0>] __kernfs_remove+0x250/0x310 [84154.213203] [<ffffffff81256470>] kernfs_remove_by_name_ns +0x50/0xc0 [84154.213203] [<ffffffff81257af5>] sysfs_remove_file_ns +0x15/0x20 [84154.213203] [<ffffffff813df339>] device_remove_file+0x19/0x20 [84154.213203] [<ffffffff813dff33>] device_remove_attrs+0x33/0x80 [84154.213203] [<ffffffff813e00a7>] device_del+0x127/0x1c0 [84154.213203] [<ffffffff813e0162>] device_unregister+0x22/0x60 [84154.213203] [<ffffffff813e66de>] unregister_cpu+0x1e/0x40 [84154.213203] [<ffffffff81009a33>] arch_unregister_cpu+0x23/0x30 [84154.213203] [<ffffffff8136f619>] acpi_processor_remove +0x8d/0xb2 [84154.213203] [<ffffffff8136cfff>] acpi_bus_trim+0x5a/0x8d [84154.213203] [<ffffffff8136ec3b>] acpi_device_hotplug +0x1a8/0x3ec [84154.213203] [<ffffffff81369002>] acpi_hotplug_work_fn +0x1f/0x2b [84154.213203] [<ffffffff8108754b>] process_one_work+0x1eb/0x6b0 [84154.213203] [<ffffffff81087e9b>] worker_thread+0x11b/0x370 [84154.213203] [<ffffffff81090324>] kthread+0xe4/0x100 [84154.213203] [<ffffffff815d2f2c>] ret_from_fork+0x7c/0xb0 [84154.213203] -> #2 (cpu_hotplug.lock#2){+.+.+.}: [84154.213203] [<ffffffff810c408b>] lock_acquire+0x9b/0x1d0 [84154.213203] [<ffffffff815c7700>] mutex_lock_nested+0x50/0x3c0 [84154.213203] [<ffffffff810665bf>] cpu_hotplug_begin+0x4f/0x80 [84154.213203] [<ffffffff8106666f>] _cpu_up+0x3f/0x160 [84154.213203] [<ffffffff810667f9>] cpu_up+0x69/0x80 [84154.213203] [<ffffffff81b18f14>] smp_init+0x60/0x8c [84154.213203] [<ffffffff81b00fd8>] kernel_init_freeable +0x126/0x23b [84154.213203] [<ffffffff815b4a3e>] kernel_init+0xe/0xf0 [84154.213203] [<ffffffff815d2f2c>] ret_from_fork+0x7c/0xb0 [84154.213203] -> #1 (cpu_hotplug.lock){++++++}: [84154.213203] [<ffffffff810c408b>] lock_acquire+0x9b/0x1d0 [84154.213203] [<ffffffff810665b1>] cpu_hotplug_begin+0x41/0x80 [84154.213203] [<ffffffff8106666f>] _cpu_up+0x3f/0x160 [84154.213203] [<ffffffff810667f9>] cpu_up+0x69/0x80 [84154.213203] [<ffffffff81b18f14>] smp_init+0x60/0x8c [84154.213203] [<ffffffff81b00fd8>] kernel_init_freeable +0x126/0x23b [84154.213203] [<ffffffff815b4a3e>] kernel_init+0xe/0xf0 [84154.213203] [<ffffffff815d2f2c>] ret_from_fork+0x7c/0xb0 [84154.213203] -> #0 (cpu_add_remove_lock){+.+.+.}: [84154.213203] [<ffffffff810c397a>] __lock_acquire+0x1f2a/0x1f60 [84154.213203] [<ffffffff810c408b>] lock_acquire+0x9b/0x1d0 [84154.213203] [<ffffffff815c7700>] mutex_lock_nested+0x50/0x3c0 [84154.213203] [<ffffffff810664a7>] cpu_maps_update_begin +0x17/0x20 [84154.213203] [<ffffffff815b582d>] cpu_down+0x1d/0x50 [84154.213203] [<ffffffff813e63b4>] cpu_subsys_offline+0x14/0x20 [84154.213203] [<ffffffff813e145d>] device_offline+0xad/0xd0 [84154.213203] [<ffffffff813e1562>] online_store+0x42/0x80 [84154.213203] [<ffffffff813deab8>] dev_attr_store+0x18/0x30 [84154.213203] [<ffffffff81257bb9>] sysfs_kf_write+0x49/0x60 [84154.213203] [<ffffffff81256e39>] kernfs_fop_write+0x109/0x190 [84154.213203] [<ffffffff811d15be>] vfs_write+0xbe/0x1c0 [84154.213203] [<ffffffff811d1a52>] SyS_write+0x52/0xb0 [84154.213203] [<ffffffff815d3162>] tracesys+0xd0/0xd5 [84154.213203] [84154.213203] other info that might help us debug this: [84154.213203] [84154.213203] Chain exists of: cpu_add_remove_lock --> cpu_hotplug.lock#2 --> s_active#79
[84154.213203] Possible unsafe locking scenario: [84154.213203] [84154.213203] CPU0 CPU1 [84154.213203] ---- ---- [84154.213203] lock(s_active#79); [84154.213203] lock(cpu_hotplug.lock#2); [84154.213203] lock(s_active#79); [84154.213203] lock(cpu_add_remove_lock); [84154.213203] [84154.213203] *** DEADLOCK *** .............
The deadlock itself seems already fixed in commit 5e33bc41.
As Tejun suggested, to avoid this lockdep warning, kernfs_break_active_protection() is used before online/offline callbacks to take the s_active lock out of the dependency chain during online/offline operations.
Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com> --- drivers/base/core.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/base/core.c b/drivers/base/core.c index 0dd6528..b313ad7 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -439,6 +439,7 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr, { bool val; int ret; + struct kernfs_node *kn; ret = strtobool(buf, &val); if (ret < 0) @@ -448,7 +449,19 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr, if (ret) return ret; + kn = kernfs_find_and_get(dev->kobj.sd, attr->attr.name); + if (WARN_ON_ONCE(!kn)) + goto out; + + get_device(dev); + kernfs_break_active_protection(kn); ret = val ? device_online(dev) : device_offline(dev); + kernfs_unbreak_active_protection(kn); + put_device(dev); + + kernfs_put(kn); + +out: unlock_device_hotplug(); return ret < 0 ? ret : count; }
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