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Fix txg_sync_thread deadlock 

Update two kmem_alloc()'s in dbuf_dirty() to use KM_PUSHPAGE.
Because these functions are called from txg_sync_thread we
must ensure they don't reenter the zfs filesystem code via
the .writepage callback.  This would result in a deadlock.

This deadlock is rare and has only been observed once under
an abusive mmap() write workload.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Brian Behlendorf 2011-07-22 13:55:27 -07:00
parent f7ef846ea1
commit beb9826902
1 changed files with 2 additions and 2 deletions
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4
module/zfs/dbuf.c
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@ -1095,7 +1095,7 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
dn->dn_dirtyctx =
(dmu_tx_is_syncing(tx) ? DN_DIRTY_SYNC : DN_DIRTY_OPEN);
ASSERT(dn->dn_dirtyctx_firstset == NULL);
dn->dn_dirtyctx_firstset = kmem_alloc(1, KM_SLEEP);
dn->dn_dirtyctx_firstset = kmem_alloc(1, KM_PUSHPAGE);
}
mutex_exit(&dn->dn_mtx);
@ -1172,7 +1172,7 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
* to make a copy of it so that the changes we make in this
* transaction group won't leak out when we sync the older txg.
*/
dr = kmem_zalloc(sizeof (dbuf_dirty_record_t), KM_SLEEP);
dr = kmem_zalloc(sizeof (dbuf_dirty_record_t), KM_PUSHPAGE);
list_link_init(&dr->dr_dirty_node);
if (db->db_level == 0) {
void *data_old = db->db_buf;