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linux/fs/xfs/xfs_extent_busy.c
Dave Chinner 292378edcb xfs: remote attribute blocks aren't really userdata 
When adding a new remote attribute, we write the attribute to the
new extent before the allocation transaction is committed. This
means we cannot reuse busy extents as that violates crash
consistency semantics. Hence we currently treat remote attribute
extent allocation like userdata because it has the same overwrite
ordering constraints as userdata.

Unfortunately, this also allows the allocator to incorrectly apply
extent size hints to the remote attribute extent allocation. This
results in interesting failures, such as transaction block
reservation overruns and in-memory inode attribute fork corruption.

To fix this, we need to separate the busy extent reuse configuration
from the userdata configuration. This changes the definition of
XFS_BMAPI_METADATA slightly - it now means that allocation is
metadata and reuse of busy extents is acceptible due to the metadata
ordering semantics of the journal. If this flag is not set, it
means the allocation is that has unordered data writeback, and hence
busy extent reuse is not allowed. It no longer implies the
allocation is for user data, just that the data write will not be
strictly ordered. This matches the semantics for both user data
and remote attribute block allocation.

As such, This patch changes the "userdata" field to a "datatype"
field, and adds a "no busy reuse" flag to the field.
When we detect an unordered data extent allocation, we immediately set
the no reuse flag. We then set the "user data" flags based on the
inode fork we are allocating the extent to. Hence we only set
userdata flags on data fork allocations now and consider attribute
fork remote extents to be an unordered metadata extent.

The result is that remote attribute extents now have the expected
allocation semantics, and the data fork allocation behaviour is
completely unchanged.

It should be noted that there may be other ways to fix this (e.g.
use ordered metadata buffers for the remote attribute extent data
write) but they are more invasive and difficult to validate both
from a design and implementation POV. Hence this patch takes the
simple, obvious route to fixing the problem...

Reported-and-tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
2016-09-26 08:21:28 +10:00

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/*
* Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
* Copyright (c) 2010 David Chinner.
* Copyright (c) 2011 Christoph Hellwig.
* All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_shared.h"
#include "xfs_trans_resv.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_alloc.h"
#include "xfs_extent_busy.h"
#include "xfs_trace.h"
#include "xfs_trans.h"
#include "xfs_log.h"
void
xfs_extent_busy_insert(
struct xfs_trans *tp,
xfs_agnumber_t agno,
xfs_agblock_t bno,
xfs_extlen_t len,
unsigned int flags)
{
struct xfs_extent_busy *new;
struct xfs_extent_busy *busyp;
struct xfs_perag *pag;
struct rb_node **rbp;
struct rb_node *parent = NULL;
new = kmem_zalloc(sizeof(struct xfs_extent_busy), KM_MAYFAIL);
if (!new) {
/*
* No Memory! Since it is now not possible to track the free
* block, make this a synchronous transaction to insure that
* the block is not reused before this transaction commits.
*/
trace_xfs_extent_busy_enomem(tp->t_mountp, agno, bno, len);
xfs_trans_set_sync(tp);
return;
}
new->agno = agno;
new->bno = bno;
new->length = len;
INIT_LIST_HEAD(&new->list);
new->flags = flags;
/* trace before insert to be able to see failed inserts */
trace_xfs_extent_busy(tp->t_mountp, agno, bno, len);
pag = xfs_perag_get(tp->t_mountp, new->agno);
spin_lock(&pag->pagb_lock);
rbp = &pag->pagb_tree.rb_node;
while (*rbp) {
parent = *rbp;
busyp = rb_entry(parent, struct xfs_extent_busy, rb_node);
if (new->bno < busyp->bno) {
rbp = &(*rbp)->rb_left;
ASSERT(new->bno + new->length <= busyp->bno);
} else if (new->bno > busyp->bno) {
rbp = &(*rbp)->rb_right;
ASSERT(bno >= busyp->bno + busyp->length);
} else {
ASSERT(0);
}
}
rb_link_node(&new->rb_node, parent, rbp);
rb_insert_color(&new->rb_node, &pag->pagb_tree);
list_add(&new->list, &tp->t_busy);
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
}
/*
* Search for a busy extent within the range of the extent we are about to
* allocate. You need to be holding the busy extent tree lock when calling
* xfs_extent_busy_search(). This function returns 0 for no overlapping busy
* extent, -1 for an overlapping but not exact busy extent, and 1 for an exact
* match. This is done so that a non-zero return indicates an overlap that
* will require a synchronous transaction, but it can still be
* used to distinguish between a partial or exact match.
*/
int
xfs_extent_busy_search(
struct xfs_mount *mp,
xfs_agnumber_t agno,
xfs_agblock_t bno,
xfs_extlen_t len)
{
struct xfs_perag *pag;
struct rb_node *rbp;
struct xfs_extent_busy *busyp;
int match = 0;
pag = xfs_perag_get(mp, agno);
spin_lock(&pag->pagb_lock);
rbp = pag->pagb_tree.rb_node;
/* find closest start bno overlap */
while (rbp) {
busyp = rb_entry(rbp, struct xfs_extent_busy, rb_node);
if (bno < busyp->bno) {
/* may overlap, but exact start block is lower */
if (bno + len > busyp->bno)
match = -1;
rbp = rbp->rb_left;
} else if (bno > busyp->bno) {
/* may overlap, but exact start block is higher */
if (bno < busyp->bno + busyp->length)
match = -1;
rbp = rbp->rb_right;
} else {
/* bno matches busyp, length determines exact match */
match = (busyp->length == len) ? 1 : -1;
break;
}
}
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
return match;
}
/*
* The found free extent [fbno, fend] overlaps part or all of the given busy
* extent. If the overlap covers the beginning, the end, or all of the busy
* extent, the overlapping portion can be made unbusy and used for the
* allocation. We can't split a busy extent because we can't modify a
* transaction/CIL context busy list, but we can update an entry's block
* number or length.
*
* Returns true if the extent can safely be reused, or false if the search
* needs to be restarted.
*/
STATIC bool
xfs_extent_busy_update_extent(
struct xfs_mount *mp,
struct xfs_perag *pag,
struct xfs_extent_busy *busyp,
xfs_agblock_t fbno,
xfs_extlen_t flen,
bool userdata) __releases(&pag->pagb_lock)
__acquires(&pag->pagb_lock)
{
xfs_agblock_t fend = fbno + flen;
xfs_agblock_t bbno = busyp->bno;
xfs_agblock_t bend = bbno + busyp->length;
/*
* This extent is currently being discarded. Give the thread
* performing the discard a chance to mark the extent unbusy
* and retry.
*/
if (busyp->flags & XFS_EXTENT_BUSY_DISCARDED) {
spin_unlock(&pag->pagb_lock);
delay(1);
spin_lock(&pag->pagb_lock);
return false;
}
/*
* If there is a busy extent overlapping a user allocation, we have
* no choice but to force the log and retry the search.
*
* Fortunately this does not happen during normal operation, but
* only if the filesystem is very low on space and has to dip into
* the AGFL for normal allocations.
*/
if (userdata)
goto out_force_log;
if (bbno < fbno && bend > fend) {
/*
* Case 1:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +---------+
* fbno fend
*/
/*
* We would have to split the busy extent to be able to track
* it correct, which we cannot do because we would have to
* modify the list of busy extents attached to the transaction
* or CIL context, which is immutable.
*
* Force out the log to clear the busy extent and retry the
* search.
*/
goto out_force_log;
} else if (bbno >= fbno && bend <= fend) {
/*
* Case 2:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-----------------+
* fbno fend
*
* Case 3:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +--------------------------+
* fbno fend
*
* Case 4:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +--------------------------+
* fbno fend
*
* Case 5:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-----------------------------------+
* fbno fend
*
*/
/*
* The busy extent is fully covered by the extent we are
* allocating, and can simply be removed from the rbtree.
* However we cannot remove it from the immutable list
* tracking busy extents in the transaction or CIL context,
* so set the length to zero to mark it invalid.
*
* We also need to restart the busy extent search from the
* tree root, because erasing the node can rearrange the
* tree topology.
*/
rb_erase(&busyp->rb_node, &pag->pagb_tree);
busyp->length = 0;
return false;
} else if (fend < bend) {
/*
* Case 6:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +---------+
* fbno fend
*
* Case 7:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +------------------+
* fbno fend
*
*/
busyp->bno = fend;
} else if (bbno < fbno) {
/*
* Case 8:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-------------+
* fbno fend
*
* Case 9:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +----------------------+
* fbno fend
*/
busyp->length = fbno - busyp->bno;
} else {
ASSERT(0);
}
trace_xfs_extent_busy_reuse(mp, pag->pag_agno, fbno, flen);
return true;
out_force_log:
spin_unlock(&pag->pagb_lock);
xfs_log_force(mp, XFS_LOG_SYNC);
trace_xfs_extent_busy_force(mp, pag->pag_agno, fbno, flen);
spin_lock(&pag->pagb_lock);
return false;
}
/*
* For a given extent [fbno, flen], make sure we can reuse it safely.
*/
void
xfs_extent_busy_reuse(
struct xfs_mount *mp,
xfs_agnumber_t agno,
xfs_agblock_t fbno,
xfs_extlen_t flen,
bool userdata)
{
struct xfs_perag *pag;
struct rb_node *rbp;
ASSERT(flen > 0);
pag = xfs_perag_get(mp, agno);
spin_lock(&pag->pagb_lock);
restart:
rbp = pag->pagb_tree.rb_node;
while (rbp) {
struct xfs_extent_busy *busyp =
rb_entry(rbp, struct xfs_extent_busy, rb_node);
xfs_agblock_t bbno = busyp->bno;
xfs_agblock_t bend = bbno + busyp->length;
if (fbno + flen <= bbno) {
rbp = rbp->rb_left;
continue;
} else if (fbno >= bend) {
rbp = rbp->rb_right;
continue;
}
if (!xfs_extent_busy_update_extent(mp, pag, busyp, fbno, flen,
userdata))
goto restart;
}
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
}
/*
* For a given extent [fbno, flen], search the busy extent list to find a
* subset of the extent that is not busy. If *rlen is smaller than
* args->minlen no suitable extent could be found, and the higher level
* code needs to force out the log and retry the allocation.
*/
void
xfs_extent_busy_trim(
struct xfs_alloc_arg *args,
xfs_agblock_t bno,
xfs_extlen_t len,
xfs_agblock_t *rbno,
xfs_extlen_t *rlen)
{
xfs_agblock_t fbno;
xfs_extlen_t flen;
struct rb_node *rbp;
ASSERT(len > 0);
spin_lock(&args->pag->pagb_lock);
restart:
fbno = bno;
flen = len;
rbp = args->pag->pagb_tree.rb_node;
while (rbp && flen >= args->minlen) {
struct xfs_extent_busy *busyp =
rb_entry(rbp, struct xfs_extent_busy, rb_node);
xfs_agblock_t fend = fbno + flen;
xfs_agblock_t bbno = busyp->bno;
xfs_agblock_t bend = bbno + busyp->length;
if (fend <= bbno) {
rbp = rbp->rb_left;
continue;
} else if (fbno >= bend) {
rbp = rbp->rb_right;
continue;
}
/*
* If this is a metadata allocation, try to reuse the busy
* extent instead of trimming the allocation.
*/
if (!xfs_alloc_is_userdata(args->datatype) &&
!(busyp->flags & XFS_EXTENT_BUSY_DISCARDED)) {
if (!xfs_extent_busy_update_extent(args->mp, args->pag,
busyp, fbno, flen,
false))
goto restart;
continue;
}
if (bbno <= fbno) {
/* start overlap */
/*
* Case 1:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +---------+
* fbno fend
*
* Case 2:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-------------+
* fbno fend
*
* Case 3:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-------------+
* fbno fend
*
* Case 4:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-----------------+
* fbno fend
*
* No unbusy region in extent, return failure.
*/
if (fend <= bend)
goto fail;
/*
* Case 5:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +----------------------+
* fbno fend
*
* Case 6:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +--------------------------+
* fbno fend
*
* Needs to be trimmed to:
* +-------+
* fbno fend
*/
fbno = bend;
} else if (bend >= fend) {
/* end overlap */
/*
* Case 7:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +------------------+
* fbno fend
*
* Case 8:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +--------------------------+
* fbno fend
*
* Needs to be trimmed to:
* +-------+
* fbno fend
*/
fend = bbno;
} else {
/* middle overlap */
/*
* Case 9:
* bbno bend
* +BBBBBBBBBBBBBBBBB+
* +-----------------------------------+
* fbno fend
*
* Can be trimmed to:
* +-------+ OR +-------+
* fbno fend fbno fend
*
* Backward allocation leads to significant
* fragmentation of directories, which degrades
* directory performance, therefore we always want to
* choose the option that produces forward allocation
* patterns.
* Preferring the lower bno extent will make the next
* request use "fend" as the start of the next
* allocation; if the segment is no longer busy at
* that point, we'll get a contiguous allocation, but
* even if it is still busy, we will get a forward
* allocation.
* We try to avoid choosing the segment at "bend",
* because that can lead to the next allocation
* taking the segment at "fbno", which would be a
* backward allocation. We only use the segment at
* "fbno" if it is much larger than the current
* requested size, because in that case there's a
* good chance subsequent allocations will be
* contiguous.
*/
if (bbno - fbno >= args->maxlen) {
/* left candidate fits perfect */
fend = bbno;
} else if (fend - bend >= args->maxlen * 4) {
/* right candidate has enough free space */
fbno = bend;
} else if (bbno - fbno >= args->minlen) {
/* left candidate fits minimum requirement */
fend = bbno;
} else {
goto fail;
}
}
flen = fend - fbno;
}
spin_unlock(&args->pag->pagb_lock);
if (fbno != bno || flen != len) {
trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len,
fbno, flen);
}
*rbno = fbno;
*rlen = flen;
return;
fail:
/*
* Return a zero extent length as failure indications. All callers
* re-check if the trimmed extent satisfies the minlen requirement.
*/
spin_unlock(&args->pag->pagb_lock);
trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len, fbno, 0);
*rbno = fbno;
*rlen = 0;
}
STATIC void
xfs_extent_busy_clear_one(
struct xfs_mount *mp,
struct xfs_perag *pag,
struct xfs_extent_busy *busyp)
{
if (busyp->length) {
trace_xfs_extent_busy_clear(mp, busyp->agno, busyp->bno,
busyp->length);
rb_erase(&busyp->rb_node, &pag->pagb_tree);
}
list_del_init(&busyp->list);
kmem_free(busyp);
}
/*
* Remove all extents on the passed in list from the busy extents tree.
* If do_discard is set skip extents that need to be discarded, and mark
* these as undergoing a discard operation instead.
*/
void
xfs_extent_busy_clear(
struct xfs_mount *mp,
struct list_head *list,
bool do_discard)
{
struct xfs_extent_busy *busyp, *n;
struct xfs_perag *pag = NULL;
xfs_agnumber_t agno = NULLAGNUMBER;
list_for_each_entry_safe(busyp, n, list, list) {
if (busyp->agno != agno) {
if (pag) {
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
}
pag = xfs_perag_get(mp, busyp->agno);
spin_lock(&pag->pagb_lock);
agno = busyp->agno;
}
if (do_discard && busyp->length &&
!(busyp->flags & XFS_EXTENT_BUSY_SKIP_DISCARD))
busyp->flags = XFS_EXTENT_BUSY_DISCARDED;
else
xfs_extent_busy_clear_one(mp, pag, busyp);
}
if (pag) {
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
}
}
/*
* Callback for list_sort to sort busy extents by the AG they reside in.
*/
int
xfs_extent_busy_ag_cmp(
void *priv,
struct list_head *a,
struct list_head *b)
{
return container_of(a, struct xfs_extent_busy, list)->agno -
container_of(b, struct xfs_extent_busy, list)->agno;
}
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