https://github.com/torvalds/linux
Revision 9230a0b65b47fe6856c4468ec0175c4987e5bede authored by Dave Chinner on 20 November 2018, 06:50:08 UTC, committed by Darrick J. Wong on 21 November 2018, 18:10:53 UTC
Long saga. There have been days spent following this through dead end after dead end in multi-GB event traces. This morning, after writing a trace-cmd wrapper that enabled me to be more selective about XFS trace points, I discovered that I could get just enough essential tracepoints enabled that there was a 50:50 chance the fsx config would fail at ~115k ops. If it didn't fail at op 115547, I stopped fsx at op 115548 anyway. That gave me two traces - one where the problem manifested, and one where it didn't. After refining the traces to have the necessary information, I found that in the failing case there was a real extent in the COW fork compared to an unwritten extent in the working case. Walking back through the two traces to the point where the CWO fork extents actually diverged, I found that the bad case had an extra unwritten extent in it. This is likely because the bug it led me to had triggered multiple times in those 115k ops, leaving stray COW extents around. What I saw was a COW delalloc conversion to an unwritten extent (as they should always be through xfs_iomap_write_allocate()) resulted in a /written extent/: xfs_writepage: dev 259:0 ino 0x83 pgoff 0x17000 size 0x79a00 offset 0 length 0 xfs_iext_remove: dev 259:0 ino 0x83 state RC|LF|RF|COW cur 0xffff888247b899c0/2 offset 32 block 152 count 20 flag 1 caller xfs_bmap_add_extent_delay_real xfs_bmap_pre_update: dev 259:0 ino 0x83 state RC|LF|RF|COW cur 0xffff888247b899c0/1 offset 1 block 4503599627239429 count 31 flag 0 caller xfs_bmap_add_extent_delay_real xfs_bmap_post_update: dev 259:0 ino 0x83 state RC|LF|RF|COW cur 0xffff888247b899c0/1 offset 1 block 121 count 51 flag 0 caller xfs_bmap_add_ex Basically, Cow fork before: 0 1 32 52 +H+DDDDDDDDDDDD+UUUUUUUUUUU+ PREV RIGHT COW delalloc conversion allocates: 1 32 +uuuuuuuuuuuu+ NEW And the result according to the xfs_bmap_post_update trace was: 0 1 32 52 +H+wwwwwwwwwwwwwwwwwwwwwwww+ PREV Which is clearly wrong - it should be a merged unwritten extent, not an unwritten extent. That lead me to look at the LEFT_FILLING|RIGHT_FILLING|RIGHT_CONTIG case in xfs_bmap_add_extent_delay_real(), and sure enough, there's the bug. It takes the old delalloc extent (PREV) and adds the length of the RIGHT extent to it, takes the start block from NEW, removes the RIGHT extent and then updates PREV with the new extent. What it fails to do is update PREV.br_state. For delalloc, this is always XFS_EXT_NORM, while in this case we are converting the delayed allocation to unwritten, so it needs to be updated to XFS_EXT_UNWRITTEN. This LF|RF|RC case does not do this, and so the resultant extent is always written. And that's the bug I've been chasing for a week - a bmap btree bug, not a reflink/dedupe/copy_file_range bug, but a BMBT bug introduced with the recent in core extent tree scalability enhancements. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
1 parent 2c30717
Tip revision: 9230a0b65b47fe6856c4468ec0175c4987e5bede authored by Dave Chinner on 20 November 2018, 06:50:08 UTC
xfs: delalloc -> unwritten COW fork allocation can go wrong
xfs: delalloc -> unwritten COW fork allocation can go wrong
Tip revision: 9230a0b
parman.c
/*
* lib/parman.c - Manager for linear priority array areas
* Copyright (c) 2017 Mellanox Technologies. All rights reserved.
* Copyright (c) 2017 Jiri Pirko <jiri@mellanox.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the names of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* Alternatively, this software may be distributed under the terms of the
* GNU General Public License ("GPL") version 2 as published by the Free
* Software Foundation.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/list.h>
#include <linux/err.h>
#include <linux/parman.h>
struct parman_algo {
int (*item_add)(struct parman *parman, struct parman_prio *prio,
struct parman_item *item);
void (*item_remove)(struct parman *parman, struct parman_prio *prio,
struct parman_item *item);
};
struct parman {
const struct parman_ops *ops;
void *priv;
const struct parman_algo *algo;
unsigned long count;
unsigned long limit_count;
struct list_head prio_list;
};
static int parman_enlarge(struct parman *parman)
{
unsigned long new_count = parman->limit_count +
parman->ops->resize_step;
int err;
err = parman->ops->resize(parman->priv, new_count);
if (err)
return err;
parman->limit_count = new_count;
return 0;
}
static int parman_shrink(struct parman *parman)
{
unsigned long new_count = parman->limit_count -
parman->ops->resize_step;
int err;
if (new_count < parman->ops->base_count)
return 0;
err = parman->ops->resize(parman->priv, new_count);
if (err)
return err;
parman->limit_count = new_count;
return 0;
}
static bool parman_prio_used(struct parman_prio *prio)
{
return !list_empty(&prio->item_list);
}
static struct parman_item *parman_prio_first_item(struct parman_prio *prio)
{
return list_first_entry(&prio->item_list,
typeof(struct parman_item), list);
}
static unsigned long parman_prio_first_index(struct parman_prio *prio)
{
return parman_prio_first_item(prio)->index;
}
static struct parman_item *parman_prio_last_item(struct parman_prio *prio)
{
return list_last_entry(&prio->item_list,
typeof(struct parman_item), list);
}
static unsigned long parman_prio_last_index(struct parman_prio *prio)
{
return parman_prio_last_item(prio)->index;
}
static unsigned long parman_lsort_new_index_find(struct parman *parman,
struct parman_prio *prio)
{
list_for_each_entry_from_reverse(prio, &parman->prio_list, list) {
if (!parman_prio_used(prio))
continue;
return parman_prio_last_index(prio) + 1;
}
return 0;
}
static void __parman_prio_move(struct parman *parman, struct parman_prio *prio,
struct parman_item *item, unsigned long to_index,
unsigned long count)
{
parman->ops->move(parman->priv, item->index, to_index, count);
}
static void parman_prio_shift_down(struct parman *parman,
struct parman_prio *prio)
{
struct parman_item *item;
unsigned long to_index;
if (!parman_prio_used(prio))
return;
item = parman_prio_first_item(prio);
to_index = parman_prio_last_index(prio) + 1;
__parman_prio_move(parman, prio, item, to_index, 1);
list_move_tail(&item->list, &prio->item_list);
item->index = to_index;
}
static void parman_prio_shift_up(struct parman *parman,
struct parman_prio *prio)
{
struct parman_item *item;
unsigned long to_index;
if (!parman_prio_used(prio))
return;
item = parman_prio_last_item(prio);
to_index = parman_prio_first_index(prio) - 1;
__parman_prio_move(parman, prio, item, to_index, 1);
list_move(&item->list, &prio->item_list);
item->index = to_index;
}
static void parman_prio_item_remove(struct parman *parman,
struct parman_prio *prio,
struct parman_item *item)
{
struct parman_item *last_item;
unsigned long to_index;
last_item = parman_prio_last_item(prio);
if (last_item == item) {
list_del(&item->list);
return;
}
to_index = item->index;
__parman_prio_move(parman, prio, last_item, to_index, 1);
list_del(&last_item->list);
list_replace(&item->list, &last_item->list);
last_item->index = to_index;
}
static int parman_lsort_item_add(struct parman *parman,
struct parman_prio *prio,
struct parman_item *item)
{
struct parman_prio *prio2;
unsigned long new_index;
int err;
if (parman->count + 1 > parman->limit_count) {
err = parman_enlarge(parman);
if (err)
return err;
}
new_index = parman_lsort_new_index_find(parman, prio);
list_for_each_entry_reverse(prio2, &parman->prio_list, list) {
if (prio2 == prio)
break;
parman_prio_shift_down(parman, prio2);
}
item->index = new_index;
list_add_tail(&item->list, &prio->item_list);
parman->count++;
return 0;
}
static void parman_lsort_item_remove(struct parman *parman,
struct parman_prio *prio,
struct parman_item *item)
{
parman_prio_item_remove(parman, prio, item);
list_for_each_entry_continue(prio, &parman->prio_list, list)
parman_prio_shift_up(parman, prio);
parman->count--;
if (parman->limit_count - parman->count >= parman->ops->resize_step)
parman_shrink(parman);
}
static const struct parman_algo parman_lsort = {
.item_add = parman_lsort_item_add,
.item_remove = parman_lsort_item_remove,
};
static const struct parman_algo *parman_algos[] = {
&parman_lsort,
};
/**
* parman_create - creates a new parman instance
* @ops: caller-specific callbacks
* @priv: pointer to a private data passed to the ops
*
* Note: all locking must be provided by the caller.
*
* Each parman instance manages an array area with chunks of entries
* with the same priority. Consider following example:
*
* item 1 with prio 10
* item 2 with prio 10
* item 3 with prio 10
* item 4 with prio 20
* item 5 with prio 20
* item 6 with prio 30
* item 7 with prio 30
* item 8 with prio 30
*
* In this example, there are 3 priority chunks. The order of the priorities
* matters, however the order of items within a single priority chunk does not
* matter. So the same array could be ordered as follows:
*
* item 2 with prio 10
* item 3 with prio 10
* item 1 with prio 10
* item 5 with prio 20
* item 4 with prio 20
* item 7 with prio 30
* item 8 with prio 30
* item 6 with prio 30
*
* The goal of parman is to maintain the priority ordering. The caller
* provides @ops with callbacks parman uses to move the items
* and resize the array area.
*
* Returns a pointer to newly created parman instance in case of success,
* otherwise it returns NULL.
*/
struct parman *parman_create(const struct parman_ops *ops, void *priv)
{
struct parman *parman;
parman = kzalloc(sizeof(*parman), GFP_KERNEL);
if (!parman)
return NULL;
INIT_LIST_HEAD(&parman->prio_list);
parman->ops = ops;
parman->priv = priv;
parman->limit_count = ops->base_count;
parman->algo = parman_algos[ops->algo];
return parman;
}
EXPORT_SYMBOL(parman_create);
/**
* parman_destroy - destroys existing parman instance
* @parman: parman instance
*
* Note: all locking must be provided by the caller.
*/
void parman_destroy(struct parman *parman)
{
WARN_ON(!list_empty(&parman->prio_list));
kfree(parman);
}
EXPORT_SYMBOL(parman_destroy);
/**
* parman_prio_init - initializes a parman priority chunk
* @parman: parman instance
* @prio: parman prio structure to be initialized
* @prority: desired priority of the chunk
*
* Note: all locking must be provided by the caller.
*
* Before caller could add an item with certain priority, he has to
* initialize a priority chunk for it using this function.
*/
void parman_prio_init(struct parman *parman, struct parman_prio *prio,
unsigned long priority)
{
struct parman_prio *prio2;
struct list_head *pos;
INIT_LIST_HEAD(&prio->item_list);
prio->priority = priority;
/* Position inside the list according to priority */
list_for_each(pos, &parman->prio_list) {
prio2 = list_entry(pos, typeof(*prio2), list);
if (prio2->priority > prio->priority)
break;
}
list_add_tail(&prio->list, pos);
}
EXPORT_SYMBOL(parman_prio_init);
/**
* parman_prio_fini - finalizes use of parman priority chunk
* @prio: parman prio structure
*
* Note: all locking must be provided by the caller.
*/
void parman_prio_fini(struct parman_prio *prio)
{
WARN_ON(parman_prio_used(prio));
list_del(&prio->list);
}
EXPORT_SYMBOL(parman_prio_fini);
/**
* parman_item_add - adds a parman item under defined priority
* @parman: parman instance
* @prio: parman prio instance to add the item to
* @item: parman item instance
*
* Note: all locking must be provided by the caller.
*
* Adds item to a array managed by parman instance under the specified priority.
*
* Returns 0 in case of success, negative number to indicate an error.
*/
int parman_item_add(struct parman *parman, struct parman_prio *prio,
struct parman_item *item)
{
return parman->algo->item_add(parman, prio, item);
}
EXPORT_SYMBOL(parman_item_add);
/**
* parman_item_del - deletes parman item
* @parman: parman instance
* @prio: parman prio instance to delete the item from
* @item: parman item instance
*
* Note: all locking must be provided by the caller.
*/
void parman_item_remove(struct parman *parman, struct parman_prio *prio,
struct parman_item *item)
{
parman->algo->item_remove(parman, prio, item);
}
EXPORT_SYMBOL(parman_item_remove);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Jiri Pirko <jiri@mellanox.com>");
MODULE_DESCRIPTION("Priority-based array manager");
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