linux/fs/xfs/xfs_filestream.c
Brian Foster f650df7171 xfs: fix soft lockup via spinning in filestream ag selection loop
The filestream AG selection loop uses pagf data to aid in AG
selection, which depends on pagf initialization. If the in-core
structure is not initialized, the caller invokes the AGF read path
to do so and carries on. If another task enters the loop and finds
a pagf init already in progress, the AGF read returns -EAGAIN and
the task continues the loop. This does not increment the current ag
index, however, which means the task spins on the current AGF buffer
until unlocked.

If the AGF read I/O submitted by the initial task happens to be
delayed for whatever reason, this results in soft lockup warnings
via the spinning task. This is reproduced by xfs/170. To avoid this
problem, fix the AGF trylock failure path to properly iterate to the
next AG. If a task iterates all AGs without making progress, the
trylock behavior is dropped in favor of blocking locks and thus a
soft lockup is no longer possible.

Fixes: f48e2df8a8 ("xfs: make xfs_*read_agf return EAGAIN to ALLOC_FLAG_TRYLOCK callers")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
2022-04-26 13:34:54 +10:00

394 lines
8.7 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2006-2007 Silicon Graphics, Inc.
* Copyright (c) 2014 Christoph Hellwig.
* All Rights Reserved.
*/
#include "xfs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_bmap.h"
#include "xfs_alloc.h"
#include "xfs_mru_cache.h"
#include "xfs_trace.h"
#include "xfs_ag.h"
#include "xfs_ag_resv.h"
#include "xfs_trans.h"
#include "xfs_filestream.h"
struct xfs_fstrm_item {
struct xfs_mru_cache_elem mru;
xfs_agnumber_t ag; /* AG in use for this directory */
};
enum xfs_fstrm_alloc {
XFS_PICK_USERDATA = 1,
XFS_PICK_LOWSPACE = 2,
};
/*
* Allocation group filestream associations are tracked with per-ag atomic
* counters. These counters allow xfs_filestream_pick_ag() to tell whether a
* particular AG already has active filestreams associated with it.
*/
int
xfs_filestream_peek_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;
pag = xfs_perag_get(mp, agno);
ret = atomic_read(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}
static int
xfs_filestream_get_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;
pag = xfs_perag_get(mp, agno);
ret = atomic_inc_return(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}
static void
xfs_filestream_put_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
pag = xfs_perag_get(mp, agno);
atomic_dec(&pag->pagf_fstrms);
xfs_perag_put(pag);
}
static void
xfs_fstrm_free_func(
void *data,
struct xfs_mru_cache_elem *mru)
{
struct xfs_mount *mp = data;
struct xfs_fstrm_item *item =
container_of(mru, struct xfs_fstrm_item, mru);
xfs_filestream_put_ag(mp, item->ag);
trace_xfs_filestream_free(mp, mru->key, item->ag);
kmem_free(item);
}
/*
* Scan the AGs starting at startag looking for an AG that isn't in use and has
* at least minlen blocks free.
*/
static int
xfs_filestream_pick_ag(
struct xfs_inode *ip,
xfs_agnumber_t startag,
xfs_agnumber_t *agp,
int flags,
xfs_extlen_t minlen)
{
struct xfs_mount *mp = ip->i_mount;
struct xfs_fstrm_item *item;
struct xfs_perag *pag;
xfs_extlen_t longest, free = 0, minfree, maxfree = 0;
xfs_agnumber_t ag, max_ag = NULLAGNUMBER;
int err, trylock, nscan;
ASSERT(S_ISDIR(VFS_I(ip)->i_mode));
/* 2% of an AG's blocks must be free for it to be chosen. */
minfree = mp->m_sb.sb_agblocks / 50;
ag = startag;
*agp = NULLAGNUMBER;
/* For the first pass, don't sleep trying to init the per-AG. */
trylock = XFS_ALLOC_FLAG_TRYLOCK;
for (nscan = 0; 1; nscan++) {
trace_xfs_filestream_scan(mp, ip->i_ino, ag);
pag = xfs_perag_get(mp, ag);
if (!pag->pagf_init) {
err = xfs_alloc_pagf_init(mp, NULL, ag, trylock);
if (err) {
if (err != -EAGAIN) {
xfs_perag_put(pag);
return err;
}
/* Couldn't lock the AGF, skip this AG. */
goto next_ag;
}
}
/* Keep track of the AG with the most free blocks. */
if (pag->pagf_freeblks > maxfree) {
maxfree = pag->pagf_freeblks;
max_ag = ag;
}
/*
* The AG reference count does two things: it enforces mutual
* exclusion when examining the suitability of an AG in this
* loop, and it guards against two filestreams being established
* in the same AG as each other.
*/
if (xfs_filestream_get_ag(mp, ag) > 1) {
xfs_filestream_put_ag(mp, ag);
goto next_ag;
}
longest = xfs_alloc_longest_free_extent(pag,
xfs_alloc_min_freelist(mp, pag),
xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE));
if (((minlen && longest >= minlen) ||
(!minlen && pag->pagf_freeblks >= minfree)) &&
(!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||
(flags & XFS_PICK_LOWSPACE))) {
/* Break out, retaining the reference on the AG. */
free = pag->pagf_freeblks;
xfs_perag_put(pag);
*agp = ag;
break;
}
/* Drop the reference on this AG, it's not usable. */
xfs_filestream_put_ag(mp, ag);
next_ag:
xfs_perag_put(pag);
/* Move to the next AG, wrapping to AG 0 if necessary. */
if (++ag >= mp->m_sb.sb_agcount)
ag = 0;
/* If a full pass of the AGs hasn't been done yet, continue. */
if (ag != startag)
continue;
/* Allow sleeping in xfs_alloc_pagf_init() on the 2nd pass. */
if (trylock != 0) {
trylock = 0;
continue;
}
/* Finally, if lowspace wasn't set, set it for the 3rd pass. */
if (!(flags & XFS_PICK_LOWSPACE)) {
flags |= XFS_PICK_LOWSPACE;
continue;
}
/*
* Take the AG with the most free space, regardless of whether
* it's already in use by another filestream.
*/
if (max_ag != NULLAGNUMBER) {
xfs_filestream_get_ag(mp, max_ag);
free = maxfree;
*agp = max_ag;
break;
}
/* take AG 0 if none matched */
trace_xfs_filestream_pick(ip, *agp, free, nscan);
*agp = 0;
return 0;
}
trace_xfs_filestream_pick(ip, *agp, free, nscan);
if (*agp == NULLAGNUMBER)
return 0;
err = -ENOMEM;
item = kmem_alloc(sizeof(*item), KM_MAYFAIL);
if (!item)
goto out_put_ag;
item->ag = *agp;
err = xfs_mru_cache_insert(mp->m_filestream, ip->i_ino, &item->mru);
if (err) {
if (err == -EEXIST)
err = 0;
goto out_free_item;
}
return 0;
out_free_item:
kmem_free(item);
out_put_ag:
xfs_filestream_put_ag(mp, *agp);
return err;
}
static struct xfs_inode *
xfs_filestream_get_parent(
struct xfs_inode *ip)
{
struct inode *inode = VFS_I(ip), *dir = NULL;
struct dentry *dentry, *parent;
dentry = d_find_alias(inode);
if (!dentry)
goto out;
parent = dget_parent(dentry);
if (!parent)
goto out_dput;
dir = igrab(d_inode(parent));
dput(parent);
out_dput:
dput(dentry);
out:
return dir ? XFS_I(dir) : NULL;
}
/*
* Find the right allocation group for a file, either by finding an
* existing file stream or creating a new one.
*
* Returns NULLAGNUMBER in case of an error.
*/
xfs_agnumber_t
xfs_filestream_lookup_ag(
struct xfs_inode *ip)
{
struct xfs_mount *mp = ip->i_mount;
struct xfs_inode *pip = NULL;
xfs_agnumber_t startag, ag = NULLAGNUMBER;
struct xfs_mru_cache_elem *mru;
ASSERT(S_ISREG(VFS_I(ip)->i_mode));
pip = xfs_filestream_get_parent(ip);
if (!pip)
return NULLAGNUMBER;
mru = xfs_mru_cache_lookup(mp->m_filestream, pip->i_ino);
if (mru) {
ag = container_of(mru, struct xfs_fstrm_item, mru)->ag;
xfs_mru_cache_done(mp->m_filestream);
trace_xfs_filestream_lookup(mp, ip->i_ino, ag);
goto out;
}
/*
* Set the starting AG using the rotor for inode32, otherwise
* use the directory inode's AG.
*/
if (xfs_is_inode32(mp)) {
xfs_agnumber_t rotorstep = xfs_rotorstep;
startag = (mp->m_agfrotor / rotorstep) % mp->m_sb.sb_agcount;
mp->m_agfrotor = (mp->m_agfrotor + 1) %
(mp->m_sb.sb_agcount * rotorstep);
} else
startag = XFS_INO_TO_AGNO(mp, pip->i_ino);
if (xfs_filestream_pick_ag(pip, startag, &ag, 0, 0))
ag = NULLAGNUMBER;
out:
xfs_irele(pip);
return ag;
}
/*
* Pick a new allocation group for the current file and its file stream.
*
* This is called when the allocator can't find a suitable extent in the
* current AG, and we have to move the stream into a new AG with more space.
*/
int
xfs_filestream_new_ag(
struct xfs_bmalloca *ap,
xfs_agnumber_t *agp)
{
struct xfs_inode *ip = ap->ip, *pip;
struct xfs_mount *mp = ip->i_mount;
xfs_extlen_t minlen = ap->length;
xfs_agnumber_t startag = 0;
int flags = 0;
int err = 0;
struct xfs_mru_cache_elem *mru;
*agp = NULLAGNUMBER;
pip = xfs_filestream_get_parent(ip);
if (!pip)
goto exit;
mru = xfs_mru_cache_remove(mp->m_filestream, pip->i_ino);
if (mru) {
struct xfs_fstrm_item *item =
container_of(mru, struct xfs_fstrm_item, mru);
startag = (item->ag + 1) % mp->m_sb.sb_agcount;
}
if (ap->datatype & XFS_ALLOC_USERDATA)
flags |= XFS_PICK_USERDATA;
if (ap->tp->t_flags & XFS_TRANS_LOWMODE)
flags |= XFS_PICK_LOWSPACE;
err = xfs_filestream_pick_ag(pip, startag, agp, flags, minlen);
/*
* Only free the item here so we skip over the old AG earlier.
*/
if (mru)
xfs_fstrm_free_func(mp, mru);
xfs_irele(pip);
exit:
if (*agp == NULLAGNUMBER)
*agp = 0;
return err;
}
void
xfs_filestream_deassociate(
struct xfs_inode *ip)
{
xfs_mru_cache_delete(ip->i_mount->m_filestream, ip->i_ino);
}
int
xfs_filestream_mount(
xfs_mount_t *mp)
{
/*
* The filestream timer tunable is currently fixed within the range of
* one second to four minutes, with five seconds being the default. The
* group count is somewhat arbitrary, but it'd be nice to adhere to the
* timer tunable to within about 10 percent. This requires at least 10
* groups.
*/
return xfs_mru_cache_create(&mp->m_filestream, mp,
xfs_fstrm_centisecs * 10, 10, xfs_fstrm_free_func);
}
void
xfs_filestream_unmount(
xfs_mount_t *mp)
{
xfs_mru_cache_destroy(mp->m_filestream);
}