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    SubjectRe: Memory corruption due to word sharing
    On Wed, Feb 01, 2012 at 04:19:18PM +0100, Jan Kara wrote:
    > We actually spotted this race in practice in btrfs on structure
    > fs/btrfs/ctree.h:struct btrfs_block_rsv where spinlock content got
    > corrupted due to update of following bitfield and there seem to be other
    > places in kernel where this could happen.

    Here's the list of structures where a bitfield is shared with spinlock
    or atomic/kref within an 8B word, generated from 3.3-rc2:

    spinlock+bitfield:

    Struct: struct ak4113; Field: init
    Struct: struct ak4114; Field: init
    Struct: struct ak4117; Field: init
    Struct: struct btrfs_block_rsv; Field: full
    Struct: struct cm109_dev; Field: buzzer_pending
    Struct: struct pch_udc_dev; Field: active
    Struct: struct rds_iw_device; Field: dma_local_lkey
    Struct: struct sierra_intf_private; Field: suspended
    Struct: struct sm501_gpio; Field: registered
    Struct: struct unix_sock; Field: gc_candidate
    Struct: struct usb_anchor; Field: poisoned
    Struct: struct usb_wwan_intf_private; Field: suspended

    atomic/kref+bitfield:

    Struct: struct dlm_lock_resource; Field: migration_pending
    Struct: struct extent_map; Field: in_tree
    Struct: struct kobject; Field: state_initialized
    Struct: struct page; Field: inuse
    Struct: struct rds_ib_connection; Field: i_flowctl
    Struct: struct rds_iw_connection; Field: i_flowctl
    Struct: struct sctp_transport; Field: dead
    Struct: struct transaction_s; Field: t_synchronous_commit
    Struct: struct xfs_ioend; Field: io_isasync


    Not all listed structs are necessarily subject to the bug. There may be
    another mechanism preventing concurrent access to the bitfield and
    spinlock/atomic, or the bitfield is modified from a single cpu, or is
    not used. But all of them need to be reviewed of course.


    david


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