• James Bottomley's avatar
    klist: fix starting point removed bug in klist iterators · 00cd29b7
    James Bottomley authored
    The starting node for a klist iteration is often passed in from
    somewhere way above the klist infrastructure, meaning there's no
    guarantee the node is still on the list.  We've seen this in SCSI where
    we use bus_find_device() to iterate through a list of devices.  In the
    face of heavy hotplug activity, the last device returned by
    bus_find_device() can be removed before the next call.  This leads to
    
    Dec  3 13:22:02 localhost kernel: WARNING: CPU: 2 PID: 28073 at include/linux/kref.h:47 klist_iter_init_node+0x3d/0x50()
    Dec  3 13:22:02 localhost kernel: Modules linked in: scsi_debug x86_pkg_temp_thermal kvm_intel kvm irqbypass crc32c_intel joydev iTCO_wdt dcdbas ipmi_devintf acpi_power_meter iTCO_vendor_support ipmi_si imsghandler pcspkr wmi acpi_cpufreq tpm_tis tpm shpchp lpc_ich mfd_core nfsd nfs_acl lockd grace sunrpc tg3 ptp pps_core
    Dec  3 13:22:02 localhost kernel: CPU: 2 PID: 28073 Comm: cat Not tainted 4.4.0-rc1+ #2
    Dec  3 13:22:02 localhost kernel: Hardware name: Dell Inc. PowerEdge R320/08VT7V, BIOS 2.0.22 11/19/2013
    Dec  3 13:22:02 localhost kernel: ffffffff81a20e77 ffff880613acfd18 ffffffff81321eef 0000000000000000
    Dec  3 13:22:02 localhost kernel: ffff880613acfd50 ffffffff8107ca52 ffff88061176b198 0000000000000000
    Dec  3 13:22:02 localhost kernel: ffffffff814542b0 ffff880610cfb100 ffff88061176b198 ffff880613acfd60
    Dec  3 13:22:02 localhost kernel: Call Trace:
    Dec  3 13:22:02 localhost kernel: [<ffffffff81321eef>] dump_stack+0x44/0x55
    Dec  3 13:22:02 localhost kernel: [<ffffffff8107ca52>] warn_slowpath_common+0x82/0xc0
    Dec  3 13:22:02 localhost kernel: [<ffffffff814542b0>] ? proc_scsi_show+0x20/0x20
    Dec  3 13:22:02 localhost kernel: [<ffffffff8107cb4a>] warn_slowpath_null+0x1a/0x20
    Dec  3 13:22:02 localhost kernel: [<ffffffff8167225d>] klist_iter_init_node+0x3d/0x50
    Dec  3 13:22:02 localhost kernel: [<ffffffff81421d41>] bus_find_device+0x51/0xb0
    Dec  3 13:22:02 localhost kernel: [<ffffffff814545ad>] scsi_seq_next+0x2d/0x40
    [...]
    
    And an eventual crash. It can actually occur in any hotplug system
    which has a device finder and a starting device.
    
    We can fix this globally by making sure the starting node for
    klist_iter_init_node() is actually a member of the list before using it
    (and by starting from the beginning if it isn't).
    Reported-by: 's avatarEwan D. Milne <emilne@redhat.com>
    Tested-by: 's avatarEwan D. Milne <emilne@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: 's avatarJames Bottomley <James.Bottomley@HansenPartnership.com>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    00cd29b7
klist.c 10.3 KB