http://bugzilla.kernel.org/show_bug.cgi?id=9731
Summary: 2.6.24-rc7: Deadlock when any ACPI eject sys node
written
Product: ACPI
Version: 2.5
KernelVersion: 2.6.24-rc7
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Other
AssignedTo: [EMAIL PROTECTED]
ReportedBy: [EMAIL PROTECTED]
Latest working kernel version: Unknown
Earliest failing kernel version: All 2.6.24-rc versions I've tried
Distribution: sles10
Hardware Environment: x86_64
Software Environment:
Problem Description:
I have "hardware" that supports ejectable CPUs. Any attempt to eject a CPU by
echoing 1 into the /sys node results in the shell doing the echo deadlocking.
Here's what dmesg says bash is doing:
bash D 0000000000000000 0 3552 3372
ffff810007023ca8 0000000000000082 0000000000000000 ffff8100014327f0
0000000000000000 ffffffff00000000 ffff81000ecde0c0 ffff8100014437c0
304a455f0dd521a0 00000000ffffdb37 00000000000000ff ffff81000fe37900
Call Trace:
[<ffffffff80447282>] wait_for_completion+0xa2/0xf0
[<ffffffff80231d50>] default_wake_function+0x0/0x10
[<ffffffff802e2f6d>] sysfs_addrm_finish+0x1dd/0x250
[<ffffffff802e17d6>] sysfs_hash_and_remove+0xa6/0xc0
[<ffffffff8038d37d>] device_remove_file+0x2d/0x60
[<ffffffff803525c3>] acpi_device_unregister+0xc8/0x124
[<ffffffff80352778>] acpi_bus_remove+0x5e/0x64
[<ffffffff803527f8>] acpi_bus_trim+0x7a/0xee
[<ffffffff803528e8>] acpi_eject_store+0x7c/0x119
[<ffffffff802e1ef4>] sysfs_write_file+0xd4/0x150
[<ffffffff80293f7d>] vfs_write+0xdd/0x150
[<ffffffff80294643>] sys_write+0x53/0x90
[<ffffffff8020bf1e>] system_call+0x7e/0x83
The problem seems to be that acpi_device_unregister tries to delete the sys
node for eject, but the node cannot be deleted until the write completes.
sysfs_write_file calls flush_write_buffer, which does this:
static int
flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t
count)
{
struct sysfs_dirent *attr_sd = dentry->d_fsdata;
struct kobject *kobj = attr_sd->s_parent->s_elem.dir.kobj;
struct sysfs_ops * ops = buffer->ops;
int rc;
/* need attr_sd for attr and ops, its parent for kobj */
if (!sysfs_get_active_two(attr_sd))
return -ENODEV;
rc = ops->store(kobj, attr_sd->s_elem.attr.attr, buffer->page, count);
sysfs_put_active_two(attr_sd);
return rc;
}
sysfs_addrm_finish calls sysfs_deactivate, which is stuck waiting forever on
the wait_for_completion call:
/**
* sysfs_deactivate - deactivate sysfs_dirent
* @sd: sysfs_dirent to deactivate
*
* Deny new active references and drain existing ones.
*/
static void sysfs_deactivate(struct sysfs_dirent *sd)
{
DECLARE_COMPLETION_ONSTACK(wait);
int v;
BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED));
sd->s_sibling = (void *)&wait;
/* atomic_add_return() is a mb(), put_active() will always see
* the updated sd->s_sibling.
*/
v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);
if (v != SD_DEACTIVATED_BIAS)
wait_for_completion(&wait);
sd->s_sibling = NULL;
}
But it looks like to me the wait_for_completion() won't return until the call
to sysfs_put_active_two() in flush_write_buffer() is invoked. This looks like
a deadlock to me.
I can provide more information if it's helpful, and can help with testing any
patches.
I'm not sure when this problem was exactly first introduced. 2.6.22 hung in a
similar way, but it looks like the code that deals with deleting sysfs nodes
got significantly reworked between 2.6.22 and 2.6.24.
Steps to reproduce:
echo 1 into any /sys/devices/LNXSYSTM:00/ACPI*/eject node. Watch the parent
process hang.
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