linux-toradex.git/fs/btrfs/delayed-ref.h, branch v5.0

btrfs: add btrfs_delete_ref_head helper

2018-12-17T13:51:46+00:00

We do this dance in cleanup_ref_head and check_ref_cleanup, unify it
into a helper and cleanup the calling functions.

Reviewed-by: Omar Sandoval 
Reviewed-by: Nikolay Borisov 
Signed-off-by: Josef Bacik 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: delayed-ref: pass delayed_refs directly to btrfs_delayed_ref_lock

2018-10-15T15:23:41+00:00

Since trans is only used for referring to delayed_refs, there is no need
to pass it instead of delayed_refs to btrfs_delayed_ref_lock().

No functional change.

Reviewed-by: Nikolay Borisov 
Signed-off-by: Lu Fengqi 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: delayed-ref: pass delayed_refs directly to btrfs_select_ref_head

2018-10-15T15:23:40+00:00

Since trans is only used for referring to delayed_refs, there is no need
to pass it instead of delayed_refs to btrfs_select_ref_head().  No
functional change.

Signed-off-by: Lu Fengqi 
Reviewed-by: Nikolay Borisov 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

Btrfs: delayed-refs: use rb_first_cached for ref_tree

2018-10-15T15:23:33+00:00

rb_first_cached() trades an extra pointer "leftmost" for doing the same
job as rb_first() but in O(1).

Functions manipulating href->ref_tree need to get the first entry, this
converts href->ref_tree to use rb_first_cached().

For more details about the optimization see patch "Btrfs: delayed-refs:
use rb_first_cached for href_root".

Tested-by: Holger Hoffstätte 
Signed-off-by: Liu Bo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

Btrfs: delayed-refs: use rb_first_cached for href_root

2018-10-15T15:23:33+00:00

rb_first_cached() trades an extra pointer "leftmost" for doing the same
job as rb_first() but in O(1).

Functions manipulating href_root need to get the first entry, this
converts href_root to use rb_first_cached().

This patch is first in the sequenct of similar updates to other rbtrees
and this is analysis of the expected behaviour and improvements.

There's a common pattern:

while (node = rb_first) {
        entry = rb_entry(node)
        next = rb_next(node)
        rb_erase(node)
        cleanup(entry)
}

rb_first needs to traverse the tree up to logN depth, rb_erase can
completely reshuffle the tree. With the caching we'll skip the traversal
in rb_first.  That's a cached memory access vs looped pointer
dereference trade-off that IMHO has a clear winner.

Measurements show there's not much difference in a sample tree with
10000 nodes: 4.5s / rb_first and 4.8s / rb_first_cached. Real effects of
caching and pointer chasing are unpredictable though.

Further optimzations can be done to avoid the expensive rb_erase step.
In some cases it's ok to process the nodes in any order, so the tree can
be traversed in post-order, not rebalancing the children nodes and just
calling free. Care must be taken regarding the next node.

Tested-by: Holger Hoffstätte 
Signed-off-by: Liu Bo 
Reviewed-by: David Sterba 
[ update changelog from mail discussions ]
Signed-off-by: David Sterba

btrfs: Remove fs_info from btrfs_add_delayed_data_ref

2018-08-06T11:12:34+00:00

This function is always called with a valid transaction handle from
where fs_info can be referenced. No functional changes.

Signed-off-by: Nikolay Borisov 
Reviewed-by: Qu Wenruo 
Signed-off-by: David Sterba

btrfs: Remove fs_info from btrfs_add_delayed_tree_ref

2018-08-06T11:12:33+00:00

This function is always called with a valid transaction handle from
where fs_info can be referenced. No functional changes.

Signed-off-by: Nikolay Borisov 
Reviewed-by: Qu Wenruo 
Signed-off-by: David Sterba

btrfs: Drop fs_info parameter from btrfs_merge_delayed_refs

2018-05-28T16:07:20+00:00

It's provided by the transaction handle.

Signed-off-by: Nikolay Borisov 
Signed-off-by: David Sterba

btrfs: Drop delayed_refs argument from btrfs_check_delayed_seq

2018-05-28T11:12:11+00:00

It's used to print its pointer in a debug statement but doesn't really
bring any useful information to the error message.

Signed-off-by: Nikolay Borisov 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: Fix race condition between delayed refs and blockgroup removal

2018-04-20T17:17:25+00:00

When the delayed refs for a head are all run, eventually
cleanup_ref_head is called which (in case of deletion) obtains a
reference for the relevant btrfs_space_info struct by querying the bg
for the range. This is problematic because when the last extent of a
bg is deleted a race window emerges between removal of that bg and the
subsequent invocation of cleanup_ref_head. This can result in cache being null
and either a null pointer dereference or assertion failure.

	task: ffff8d04d31ed080 task.stack: ffff9e5dc10cc000
	RIP: 0010:assfail.constprop.78+0x18/0x1a [btrfs]
	RSP: 0018:ffff9e5dc10cfbe8 EFLAGS: 00010292
	RAX: 0000000000000044 RBX: 0000000000000000 RCX: 0000000000000000
	RDX: ffff8d04ffc1f868 RSI: ffff8d04ffc178c8 RDI: ffff8d04ffc178c8
	RBP: ffff8d04d29e5ea0 R08: 00000000000001f0 R09: 0000000000000001
	R10: ffff9e5dc0507d58 R11: 0000000000000001 R12: ffff8d04d29e5ea0
	R13: ffff8d04d29e5f08 R14: ffff8d04efe29b40 R15: ffff8d04efe203e0
	FS:  00007fbf58ead500(0000) GS:ffff8d04ffc00000(0000) knlGS:0000000000000000
	CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	CR2: 00007fe6c6975648 CR3: 0000000013b2a000 CR4: 00000000000006f0
	DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
	DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
	Call Trace:
	 __btrfs_run_delayed_refs+0x10e7/0x12c0 [btrfs]
	 btrfs_run_delayed_refs+0x68/0x250 [btrfs]
	 btrfs_should_end_transaction+0x42/0x60 [btrfs]
	 btrfs_truncate_inode_items+0xaac/0xfc0 [btrfs]
	 btrfs_evict_inode+0x4c6/0x5c0 [btrfs]
	 evict+0xc6/0x190
	 do_unlinkat+0x19c/0x300
	 do_syscall_64+0x74/0x140
	 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
	RIP: 0033:0x7fbf589c57a7

To fix this, introduce a new flag "is_system" to head_ref structs,
which is populated at insertion time. This allows to decouple the
querying for the spaceinfo from querying the possibly deleted bg.

Fixes: d7eae3403f46 ("Btrfs: rework delayed ref total_bytes_pinned accounting")
CC: stable@vger.kernel.org # 4.14+
Suggested-by: Omar Sandoval 
Signed-off-by: Nikolay Borisov 
Reviewed-by: Omar Sandoval 
Signed-off-by: David Sterba