• Robert Richter's avatar
    oprofile: fix crash when accessing freed task structs · 750d857c
    Robert Richter authored
    This patch fixes a crash during shutdown reported below. The crash is
    caused by accessing already freed task structs. The fix changes the
    order for registering and unregistering notifier callbacks.
    
    All notifiers must be initialized before buffers start working. To
    stop buffer synchronization we cancel all workqueues, unregister the
    notifier callback and then flush all buffers. After all of this we
    finally can free all tasks listed.
    
    This should avoid accessing freed tasks.
    
    On 22.07.10 01:14:40, Benjamin Herrenschmidt wrote:
    
    > So the initial observation is a spinlock bad magic followed by a crash
    > in the spinlock debug code:
    >
    > [ 1541.586531] BUG: spinlock bad magic on CPU#5, events/5/136
    > [ 1541.597564] Unable to handle kernel paging request for data at address 0x6b6b6b6b6b6b6d03
    >
    > Backtrace looks like:
    >
    >       spin_bug+0x74/0xd4
    >       ._raw_spin_lock+0x48/0x184
    >       ._spin_lock+0x10/0x24
    >       .get_task_mm+0x28/0x8c
    >       .sync_buffer+0x1b4/0x598
    >       .wq_sync_buffer+0xa0/0xdc
    >       .worker_thread+0x1d8/0x2a8
    >       .kthread+0xa8/0xb4
    >       .kernel_thread+0x54/0x70
    >
    > So we are accessing a freed task struct in the work queue when
    > processing the samples.
    Reported-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: stable@kernel.org
    Signed-off-by: default avatarRobert Richter <robert.richter@amd.com>
    750d857c
buffer_sync.c 13.5 KB