• Robert Richter's avatar
    oprofile, dcookies: Fix possible circular locking dependency · fe47ae7f
    Robert Richter authored
    The lockdep warning below detects a possible A->B/B->A locking
    dependency of mm->mmap_sem and dcookie_mutex. The order in
    sync_buffer() is mm->mmap_sem/dcookie_mutex, while in
    sys_lookup_dcookie() it is vice versa.
    
    Fixing it in sys_lookup_dcookie() by unlocking dcookie_mutex before
    copy_to_user().
    
    oprofiled/4432 is trying to acquire lock:
     (&mm->mmap_sem){++++++}, at: [<ffffffff810b444b>] might_fault+0x53/0xa3
    
    but task is already holding lock:
     (dcookie_mutex){+.+.+.}, at: [<ffffffff81124d28>] sys_lookup_dcookie+0x45/0x149
    
    which lock already depends on the new lock.
    
    the existing dependency chain (in reverse order) is:
    
    -> #1 (dcookie_mutex){+.+.+.}:
           [<ffffffff8106557f>] lock_acquire+0xf8/0x11e
           [<ffffffff814634f0>] mutex_lock_nested+0x63/0x309
           [<ffffffff81124e5c>] get_dcookie+0x30/0x144
           [<ffffffffa0000fba>] sync_buffer+0x196/0x3ec [oprofile]
           [<ffffffffa0001226>] task_exit_notify+0x16/0x1a [oprofile]
           [<ffffffff81467b96>] notifier_call_chain+0x37/0x63
           [<ffffffff8105803d>] __blocking_notifier_call_chain+0x50/0x67
           [<ffffffff81058068>] blocking_notifier_call_chain+0x14/0x16
           [<ffffffff8105a718>] profile_task_exit+0x1a/0x1c
           [<ffffffff81039e8f>] do_exit+0x2a/0x6fc
           [<ffffffff8103a5e4>] do_group_exit+0x83/0xae
           [<ffffffff8103a626>] sys_exit_group+0x17/0x1b
           [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b
    
    -> #0 (&mm->mmap_sem){++++++}:
           [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711
           [<ffffffff8106557f>] lock_acquire+0xf8/0x11e
           [<ffffffff810b4478>] might_fault+0x80/0xa3
           [<ffffffff81124de7>] sys_lookup_dcookie+0x104/0x149
           [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b
    
    other info that might help us debug this:
    
    1 lock held by oprofiled/4432:
     #0:  (dcookie_mutex){+.+.+.}, at: [<ffffffff81124d28>] sys_lookup_dcookie+0x45/0x149
    
    stack backtrace:
    Pid: 4432, comm: oprofiled Not tainted 2.6.39-00008-ge5a450d #9
    Call Trace:
     [<ffffffff81063193>] print_circular_bug+0xae/0xbc
     [<ffffffff81064dfb>] __lock_acquire+0x1085/0x1711
     [<ffffffff8102ef13>] ? get_parent_ip+0x11/0x42
     [<ffffffff810b444b>] ? might_fault+0x53/0xa3
     [<ffffffff8106557f>] lock_acquire+0xf8/0x11e
     [<ffffffff810b444b>] ? might_fault+0x53/0xa3
     [<ffffffff810d7d54>] ? path_put+0x22/0x27
     [<ffffffff810b4478>] might_fault+0x80/0xa3
     [<ffffffff810b444b>] ? might_fault+0x53/0xa3
     [<ffffffff81124de7>] sys_lookup_dcookie+0x104/0x149
     [<ffffffff8146ad4b>] system_call_fastpath+0x16/0x1b
    
    References: https://bugzilla.kernel.org/show_bug.cgi?id=13809
    Cc: <stable@kernel.org> # .27+
    Signed-off-by: default avatarRobert Richter <robert.richter@amd.com>
    fe47ae7f
dcookies.c 6.82 KB