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author | Brian Behlendorf <[email protected]> | 2015-12-16 11:28:15 -0800 |
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committer | Brian Behlendorf <[email protected]> | 2015-12-18 13:27:12 -0800 |
commit | 6fe53787f38f10956b8d375133ed4559f8ce847b (patch) | |
tree | cdeeba055e332d5164459982896e7da020769770 /module/zfs/dmu_send.c | |
parent | a8ad3bf02cace90c45bc25df1bff1089d19e79f1 (diff) |
Fix vdev_queue_aggregate() deadlock
This deadlock may manifest itself in slightly different ways but
at the core it is caused by a memory allocation blocking on file-
system reclaim in the zio pipeline. This is normally impossible
because zio_execute() disables filesystem reclaim by setting
PF_FSTRANS on the thread. However, kmem cache allocations may
still indirectly block on file system reclaim while holding the
critical vq->vq_lock as shown below.
To resolve this issue zio_buf_alloc_flags() is introduced which
allocation flags to be passed. This can then be used in
vdev_queue_aggregate() with KM_NOSLEEP when allocating the
aggregate IO buffer. Since aggregating the IO is purely a
performance optimization we want this to either succeed or fail
quickly. Trying too hard to allocate this memory under the
vq->vq_lock can negatively impact performance and result in
this deadlock.
* z_wr_iss
zio_vdev_io_start
vdev_queue_io -> Takes vq->vq_lock
vdev_queue_io_to_issue
vdev_queue_aggregate
zio_buf_alloc -> Waiting on spl_kmem_cache process
* z_wr_int
zio_vdev_io_done
vdev_queue_io_done
mutex_lock -> Waiting on vq->vq_lock held by z_wr_iss
* txg_sync
spa_sync
dsl_pool_sync
zio_wait -> Waiting on zio being handled by z_wr_int
* spl_kmem_cache
spl_cache_grow_work
kv_alloc
spl_vmalloc
...
evict
zpl_evict_inode
zfs_inactive
dmu_tx_wait
txg_wait_open -> Waiting on txg_sync
Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Chunwei Chen <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Closes #3808
Closes #3867
Diffstat (limited to 'module/zfs/dmu_send.c')
0 files changed, 0 insertions, 0 deletions