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authorWaiman Long <longman@redhat.com>2018-09-14 14:53:32 -0400
committerVinod Koul <vkoul@kernel.org>2018-09-18 12:19:36 -0700
commitcfb03be6c7e8a1591285849c361d67b09f5149f7 (patch)
tree980c0758ac13a9d9858df6de488ac5fd914057fa /drivers/dma
parent7645d26f3b35c2bd6e0e1d3867636e5bdad97b1b (diff)
downloadblackbird-op-linux-cfb03be6c7e8a1591285849c361d67b09f5149f7.tar.gz
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driver/dma/ioat: Call del_timer_sync() without holding prep_lock
The following lockdep splat was observed: [ 1222.241750] ====================================================== [ 1222.271301] WARNING: possible circular locking dependency detected [ 1222.301060] 4.16.0-10.el8+5.x86_64+debug #1 Not tainted [ 1222.326659] ------------------------------------------------------ [ 1222.356565] systemd-shutdow/1 is trying to acquire lock: [ 1222.382660] ((&ioat_chan->timer)){+.-.}, at: [<00000000f71e1a28>] del_timer_sync+0x5/0xf0 [ 1222.422928] [ 1222.422928] but task is already holding lock: [ 1222.451743] (&(&ioat_chan->prep_lock)->rlock){+.-.}, at: [<000000008ea98b12>] ioat_shutdown+0x86/0x100 [ioatdma] : [ 1223.524987] Chain exists of: [ 1223.524987] (&ioat_chan->timer) --> &(&ioat_chan->cleanup_lock)->rlock --> &(&ioat_chan->prep_lock)->rlock [ 1223.524987] [ 1223.594082] Possible unsafe locking scenario: [ 1223.594082] [ 1223.622630] CPU0 CPU1 [ 1223.645080] ---- ---- [ 1223.667404] lock(&(&ioat_chan->prep_lock)->rlock); [ 1223.691535] lock(&(&ioat_chan->cleanup_lock)->rlock); [ 1223.728657] lock(&(&ioat_chan->prep_lock)->rlock); [ 1223.765122] lock((&ioat_chan->timer)); [ 1223.784095] [ 1223.784095] *** DEADLOCK *** [ 1223.784095] [ 1223.813492] 4 locks held by systemd-shutdow/1: [ 1223.834677] #0: (reboot_mutex){+.+.}, at: [<0000000056d33456>] SYSC_reboot+0x10f/0x300 [ 1223.873310] #1: (&dev->mutex){....}, at: [<00000000258dfdd7>] device_shutdown+0x1c8/0x660 [ 1223.913604] #2: (&dev->mutex){....}, at: [<0000000068331147>] device_shutdown+0x1d6/0x660 [ 1223.954000] #3: (&(&ioat_chan->prep_lock)->rlock){+.-.}, at: [<000000008ea98b12>] ioat_shutdown+0x86/0x100 [ioatdma] In the ioat_shutdown() function: spin_lock_bh(&ioat_chan->prep_lock); set_bit(IOAT_CHAN_DOWN, &ioat_chan->state); del_timer_sync(&ioat_chan->timer); spin_unlock_bh(&ioat_chan->prep_lock); According to the synchronization rule for the del_timer_sync() function, the caller must not hold locks which would prevent completion of the timer's handler. The timer structure has its own lock that manages its synchronization. Setting the IOAT_CHAN_DOWN bit should prevent other CPUs from trying to use that device anyway, there is probably no need to call del_timer_sync() while holding the prep_lock. So the del_timer_sync() call is now moved outside of the prep_lock critical section to prevent the circular lock dependency. Signed-off-by: Waiman Long <longman@redhat.com> Reviewed-by: Dave Jiang <dave.jiang@intel.com> Signed-off-by: Vinod Koul <vkoul@kernel.org>
Diffstat (limited to 'drivers/dma')
-rw-r--r--drivers/dma/ioat/init.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/drivers/dma/ioat/init.c b/drivers/dma/ioat/init.c
index 4fa4c06c9edb..21a5708985bc 100644
--- a/drivers/dma/ioat/init.c
+++ b/drivers/dma/ioat/init.c
@@ -1205,8 +1205,15 @@ static void ioat_shutdown(struct pci_dev *pdev)
spin_lock_bh(&ioat_chan->prep_lock);
set_bit(IOAT_CHAN_DOWN, &ioat_chan->state);
- del_timer_sync(&ioat_chan->timer);
spin_unlock_bh(&ioat_chan->prep_lock);
+ /*
+ * Synchronization rule for del_timer_sync():
+ * - The caller must not hold locks which would prevent
+ * completion of the timer's handler.
+ * So prep_lock cannot be held before calling it.
+ */
+ del_timer_sync(&ioat_chan->timer);
+
/* this should quiesce then reset */
ioat_reset_hw(ioat_chan);
}
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