tree 18a39d2da8e315ce1d6bb52527f065c05158fd51
parent 3e9fc9129e553b54933bec2a30fed29131cd6d80
author Tomasz Figa <tfiga@chromium.org> 1532794007 +0900
committer Tim Detwiler <tjdetwiler@google.com> 1539128192 -0700

CHROMIUM: virtio/wl: Fix locking order in do_new()

Fix following lockdep splat. It is a false positive, since the vfd->lock
belongs to a vfd just created and nobody else could reference it, but it
confuses lock debugging tools and the fix is trivial, so just fix it.

[    4.634549] ======================================================
[    4.634549] WARNING: possible circular locking dependency detected
[    4.634551] 4.14.58-06408-ge3d9dad0bb21 #10 Not tainted
[    4.634551] ------------------------------------------------------
[    4.634552] kworker/0:2/144 is trying to acquire lock:
[    4.634552]  (&vfd->lock){+.+.}, at: [<ffffffff814c889a>] vq_in_work_handler+0x1ac/0x366
[    4.634567]
[    4.634567] but task is already holding lock:
[    4.634567]  (&vi->vfds_lock){+.+.}, at: [<ffffffff814c8877>] vq_in_work_handler+0x189/0x366
[    4.634570]
[    4.634570] which lock already depends on the new lock.
[    4.634570]
[    4.634570]
[    4.634570] the existing dependency chain (in reverse order) is:
[    4.634571]
[    4.634571] -> #1 (&vi->vfds_lock){+.+.}:
[    4.634579]        __mutex_lock+0x81/0x39d
[    4.634580]        do_new+0x95/0x276
[    4.634581]        virtwl_ioctl_ptr+0x14c/0x20f
[    4.634588]        compat_SyS_ioctl+0x50d/0x1d0d
[    4.634591]        do_fast_syscall_32+0xbb/0xff
[    4.634593]        entry_SYSENTER_compat+0x84/0x96
[    4.634593]
[    4.634593] -> #0 (&vfd->lock){+.+.}:
[    4.634599]        lock_acquire+0x185/0x1bf
[    4.634600]        __mutex_lock+0x81/0x39d
[    4.634602]        vq_in_work_handler+0x1ac/0x366
[    4.634604]        process_one_work+0x2aa/0x4d8
[    4.634605]        worker_thread+0x193/0x24b
[    4.634606]        kthread+0xf8/0x100
[    4.634608]        ret_from_fork+0x3a/0x50
[    4.634608]
[    4.634608] other info that might help us debug this:
[    4.634608]
[    4.634609]  Possible unsafe locking scenario:
[    4.634609]
[    4.634609]        CPU0                    CPU1
[    4.634609]        ----                    ----
[    4.634610]   lock(&vi->vfds_lock);
[    4.634610]                                lock(&vfd->lock);
[    4.634611]                                lock(&vi->vfds_lock);
[    4.634612]   lock(&vfd->lock);
[    4.634613]
[    4.634613]  *** DEADLOCK ***
[    4.634613]
[    4.634614] 3 locks held by kworker/0:2/144:
[    4.634614]  #0:  ("events"){+.+.}, at: [<ffffffff810d1486>] process_one_work+0x146/0x4d8
[    4.634617]  #1:  ((&vi->in_vq_work)){+.+.}, at: [<ffffffff810d1486>] process_one_work+0x146/0x4d8
[    4.634619]  #2:  (&vi->vfds_lock){+.+.}, at: [<ffffffff814c8877>] vq_in_work_handler+0x189/0x366
[    4.634621]
[    4.634621] stack backtrace:
[    4.634623] CPU: 0 PID: 144 Comm: kworker/0:2 Not tainted 4.14.58-06408-ge3d9dad0bb21 #10
[    4.634625] Workqueue: events vq_in_work_handler
[    4.634626] Call Trace:
[    4.634630]  dump_stack+0x9f/0xd5
[    4.634632]  print_circular_bug.isra.42+0x1c7/0x1d4
[    4.634634]  __lock_acquire+0xbbd/0xe7d
[    4.634637]  ? vq_in_work_handler+0x1ac/0x366
[    4.634638]  ? lock_acquire+0x185/0x1bf
[    4.634639]  lock_acquire+0x185/0x1bf
[    4.634641]  ? vq_in_work_handler+0x1ac/0x366
[    4.634642]  __mutex_lock+0x81/0x39d
[    4.634643]  ? vq_in_work_handler+0x1ac/0x366
[    4.634645]  ? vq_in_work_handler+0x1ac/0x366
[    4.634647]  ? vq_in_work_handler+0x1ac/0x366
[    4.634648]  vq_in_work_handler+0x1ac/0x366
[    4.634650]  process_one_work+0x2aa/0x4d8
[    4.634651]  ? worker_thread+0x1d0/0x24b
[    4.634653]  ? rescuer_thread+0x2ab/0x2ab
[    4.634654]  worker_thread+0x193/0x24b
[    4.634655]  ? rescuer_thread+0x2ab/0x2ab
[    4.634656]  kthread+0xf8/0x100
[    4.634658]  ? kthread_create_on_node+0x5d/0x5d
[    4.634659]  ? do_fast_syscall_32+0xbb/0xff
[    4.634661]  ? SyS_exit_group+0xb/0xb
[    4.634662]  ret_from_fork+0x3a/0x50

BUG=none
TEST=Enable CONFIG_PROVE_LOCKING and do not see the splat anymore

Change-Id: I24d2f01bf8266fd6ae4bc558cf52295fe3b07773
Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1154233
Reviewed-by: Zach Reizner <zachr@chromium.org>