On Fri, 11 Jan 2008 09:38:25 -0800 (PST) bugme-daemon@xxxxxxxxxxxxxxxxxxx wrote: > 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: acpi_other@xxxxxxxxxxxxxxxxxxxx > ReportedBy: arai@xxxxxxxxxx > > > 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. Thanks. So it would seem that sysfs core changes caused the acpi code to fail. - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
