Greetings, I got this warning when doing writeback tests. It happens quite often in 3.6.0-rc1 as well as in 3.5.0. [ 644.273874] btrfs: block rsv returned -28 [ 644.278161] ------------[ cut here ]------------ [ 644.283050] WARNING: at /c/wfg/tip/fs/btrfs/extent-tree.c:6330 btrfs_alloc_free_block+0xd6/0x28b() [ 644.292468] Hardware name: X7DW3 [ 644.295950] Modules linked in: [ 644.299330] Pid: 10214, comm: btrfs-transacti Not tainted 3.6.0-rc1+ #4 [ 644.306201] Call Trace: [ 644.308916] [<ffffffff810697ee>] warn_slowpath_common+0x83/0x9c [ 644.315183] [<ffffffff81069821>] warn_slowpath_null+0x1a/0x1c [ 644.321274] [<ffffffff8133246f>] btrfs_alloc_free_block+0xd6/0x28b [ 644.327796] [<ffffffff81141973>] ? kfree+0x55/0x101 [ 644.333020] [<ffffffff813218ac>] __btrfs_cow_block+0x118/0x43d [ 644.339196] [<ffffffff8133c00e>] ? btrfs_buffer_uptodate+0x49/0x5f [ 644.345717] [<ffffffff81321d17>] btrfs_cow_block+0x146/0x1ac [ 644.351722] [<ffffffff81367396>] ? btrfs_set_lock_blocking_rw+0xa9/0xf7 [ 644.358677] [<ffffffff813253a6>] btrfs_search_slot+0x2e1/0x784 [ 644.364853] [<ffffffff8133753f>] btrfs_del_csums+0xee/0x2e2 [ 644.370772] [<ffffffff8132cedd>] __btrfs_free_extent+0x5b3/0x60b [ 644.377129] [<ffffffff81330c5d>] run_clustered_refs+0x79b/0x85f [ 644.383390] [<ffffffff81330fb3>] btrfs_run_delayed_refs+0x292/0x3ed [ 644.390001] [<ffffffff8197c2eb>] ? mutex_unlock+0xe/0x10 [ 644.395658] [<ffffffff81352284>] ? btrfs_run_ordered_operations+0x1a4/0x1b3 [ 644.402966] [<ffffffff813400b6>] btrfs_commit_transaction+0x94/0x995 [ 644.409664] [<ffffffff8108a996>] ? __init_waitqueue_head+0x33/0x33 [ 644.416185] [<ffffffff8107757a>] ? usleep_range+0x42/0x42 [ 644.421931] [<ffffffff8133a0bc>] transaction_kthread+0xec/0x1b3 [ 644.428192] [<ffffffff81339fd0>] ? cleaner_kthread+0xe8/0xe8 [ 644.434195] [<ffffffff8108a09b>] kthread+0x8b/0x93 [ 644.439333] [<ffffffff819863c4>] kernel_thread_helper+0x4/0x10 [ 644.445509] [<ffffffff8197e7dd>] ? retint_restore_args+0x13/0x13 [ 644.451857] [<ffffffff8108a010>] ? __init_kthread_worker+0x39/0x39 [ 644.458379] [<ffffffff819863c0>] ? gs_change+0x13/0x13 [ 644.463861] ---[ end trace 10c6b128620d1b3b ]--- [ 644.468767] btrfs: block rsv returned -28 [ 644.473041] ------------[ cut here ]------------ [ 644.477917] WARNING: at /c/wfg/tip/fs/btrfs/extent-tree.c:6330 btrfs_alloc_free_block+0xd6/0x28b() [ 644.487339] Hardware name: X7DW3 [ 644.490828] Modules linked in: [ 644.494214] Pid: 10214, comm: btrfs-transacti Tainted: G W 3.6.0-rc1+ #4 [ 644.502254] Call Trace: [ 644.504957] [<ffffffff810697ee>] warn_slowpath_common+0x83/0x9c [ 644.511221] [<ffffffff81069821>] warn_slowpath_null+0x1a/0x1c [ 644.517314] [<ffffffff8133246f>] btrfs_alloc_free_block+0xd6/0x28b [ 644.523833] [<ffffffff81141973>] ? kfree+0x55/0x101 [ 644.529057] [<ffffffff813218ac>] __btrfs_cow_block+0x118/0x43d [ 644.535235] [<ffffffff8133c00e>] ? btrfs_buffer_uptodate+0x49/0x5f [ 644.541756] [<ffffffff81321d17>] btrfs_cow_block+0x146/0x1ac [ 644.547761] [<ffffffff81367396>] ? btrfs_set_lock_blocking_rw+0xa9/0xf7 [ 644.554714] [<ffffffff813253a6>] btrfs_search_slot+0x2e1/0x784 [ 644.560892] [<ffffffff8133753f>] btrfs_del_csums+0xee/0x2e2 [ 644.566811] [<ffffffff8132cedd>] __btrfs_free_extent+0x5b3/0x60b [ 644.573168] [<ffffffff81330c5d>] run_clustered_refs+0x79b/0x85f [ 644.579439] [<ffffffff81330fb3>] btrfs_run_delayed_refs+0x292/0x3ed [ 644.586057] [<ffffffff8197c2eb>] ? mutex_unlock+0xe/0x10 [ 644.591712] [<ffffffff81352284>] ? btrfs_run_ordered_operations+0x1a4/0x1b3 [ 644.599016] [<ffffffff813400b6>] btrfs_commit_transaction+0x94/0x995 [ 644.605709] [<ffffffff8108a996>] ? __init_waitqueue_head+0x33/0x33 [ 644.612233] [<ffffffff8107757a>] ? usleep_range+0x42/0x42 [ 644.617979] [<ffffffff8133a0bc>] transaction_kthread+0xec/0x1b3 [ 644.624239] [<ffffffff81339fd0>] ? cleaner_kthread+0xe8/0xe8 [ 644.630241] [<ffffffff8108a09b>] kthread+0x8b/0x93 [ 644.635378] [<ffffffff819863c4>] kernel_thread_helper+0x4/0x10 [ 644.641555] [<ffffffff8197e7dd>] ? retint_restore_args+0x13/0x13 [ 644.647905] [<ffffffff8108a010>] ? __init_kthread_worker+0x39/0x39 [ 644.654428] [<ffffffff819863c0>] ? gs_change+0x13/0x13 [ 644.659910] ---[ end trace 10c6b128620d1b3c ]--- [ 651.834616] use_block_rsv: 2039 callbacks suppressed Thanks, Fengguang