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xfs: switch (back) to a per-buftarg buffer hash

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The per-AG buffer hashes were added when all buffer lookups took a
per-hash look.  Since then we've made lookups entirely lockless and
removed the need for a hash-wide lock for inserts and removals as
well.  With this there is no need to sharding the hash, so reduce the
used resources by using a per-buftarg hash for all buftargs.

Long after writing this initially, syzbot found a problem in the buffer
cache teardown order, which this happens to fix as well by doing the
entire buffer cache teardown in one places instead of splitting it
between destroying the buftarg and the perag structures.

Link: https://lore.kernel.org/linux-xfs/aLeUdemAZ5wmtZel@dread.disaster.area/
Reported-by: syzbot+0391d34e801643e2809b@syzkaller.appspotmail.com
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: syzbot+0391d34e801643e2809b@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Christoph Hellwig
2026-03-23 08:50:53 +01:00
committed by Carlos Maiolino
parent d02ee47bbe
commit 497560b9ef
5 changed files with 18 additions and 69 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
fs/xfs/libxfs/xfs_ag.c
View File

@@ -110,10 +110,7 @@ xfs_perag_uninit(
struct xfs_group *xg)
{
#ifdef __KERNEL__
struct xfs_perag *pag = to_perag(xg);
cancel_delayed_work_sync(&pag->pag_blockgc_work);
xfs_buf_cache_destroy(&pag->pag_bcache);
cancel_delayed_work_sync(&to_perag(xg)->pag_blockgc_work);
#endif
}
@@ -235,10 +232,6 @@ xfs_perag_alloc(
INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
#endif /* __KERNEL__ */
error = xfs_buf_cache_init(&pag->pag_bcache);
if (error)
goto out_free_perag;
/*
* Pre-calculated geometry
*/
@@ -250,12 +243,10 @@ xfs_perag_alloc(
error = xfs_group_insert(mp, pag_group(pag), index, XG_TYPE_AG);
if (error)
goto out_buf_cache_destroy;
goto out_free_perag;
return 0;
out_buf_cache_destroy:
xfs_buf_cache_destroy(&pag->pag_bcache);
out_free_perag:
kfree(pag);
return error;

2
fs/xfs/libxfs/xfs_ag.h
View File

@@ -85,8 +85,6 @@ struct xfs_perag {
int pag_ici_reclaimable; /* reclaimable inodes */
unsigned long pag_ici_reclaim_cursor; /* reclaim restart point */
struct xfs_buf_cache pag_bcache;
/* background prealloc block trimming */
struct delayed_work pag_blockgc_work;
#endif /* __KERNEL__ */

51
fs/xfs/xfs_buf.c
View File

@@ -363,20 +363,6 @@ static const struct rhashtable_params xfs_buf_hash_params = {
.obj_cmpfn = _xfs_buf_obj_cmp,
};
int
xfs_buf_cache_init(
struct xfs_buf_cache *bch)
{
return rhashtable_init(&bch->bc_hash, &xfs_buf_hash_params);
}
void
xfs_buf_cache_destroy(
struct xfs_buf_cache *bch)
{
rhashtable_destroy(&bch->bc_hash);
}
static int
xfs_buf_map_verify(
struct xfs_buftarg *btp,
@@ -434,7 +420,7 @@ xfs_buf_find_lock(
static inline int
xfs_buf_lookup(
struct xfs_buf_cache *bch,
struct xfs_buftarg *btp,
struct xfs_buf_map *map,
xfs_buf_flags_t flags,
struct xfs_buf **bpp)
@@ -443,7 +429,7 @@ xfs_buf_lookup(
int error;
rcu_read_lock();
bp = rhashtable_lookup(&bch->bc_hash, map, xfs_buf_hash_params);
bp = rhashtable_lookup(&btp->bt_hash, map, xfs_buf_hash_params);
if (!bp || !lockref_get_not_dead(&bp->b_lockref)) {
rcu_read_unlock();
return -ENOENT;
@@ -468,7 +454,6 @@ xfs_buf_lookup(
static int
xfs_buf_find_insert(
struct xfs_buftarg *btp,
struct xfs_buf_cache *bch,
struct xfs_perag *pag,
struct xfs_buf_map *cmap,
struct xfs_buf_map *map,
@@ -488,7 +473,7 @@ xfs_buf_find_insert(
new_bp->b_pag = pag;
rcu_read_lock();
bp = rhashtable_lookup_get_insert_fast(&bch->bc_hash,
bp = rhashtable_lookup_get_insert_fast(&btp->bt_hash,
&new_bp->b_rhash_head, xfs_buf_hash_params);
if (IS_ERR(bp)) {
rcu_read_unlock();
@@ -530,16 +515,6 @@ xfs_buftarg_get_pag(
return xfs_perag_get(mp, xfs_daddr_to_agno(mp, map->bm_bn));
}
static inline struct xfs_buf_cache *
xfs_buftarg_buf_cache(
struct xfs_buftarg *btp,
struct xfs_perag *pag)
{
if (pag)
return &pag->pag_bcache;
return btp->bt_cache;
}
/*
* Assembles a buffer covering the specified range. The code is optimised for
* cache hits, as metadata intensive workloads will see 3 orders of magnitude
@@ -553,7 +528,6 @@ xfs_buf_get_map(
xfs_buf_flags_t flags,
struct xfs_buf **bpp)
{
struct xfs_buf_cache *bch;
struct xfs_perag *pag;
struct xfs_buf *bp = NULL;
struct xfs_buf_map cmap = { .bm_bn = map[0].bm_bn };
@@ -570,9 +544,8 @@ xfs_buf_get_map(
return error;
pag = xfs_buftarg_get_pag(btp, &cmap);
bch = xfs_buftarg_buf_cache(btp, pag);
error = xfs_buf_lookup(bch, &cmap, flags, &bp);
error = xfs_buf_lookup(btp, &cmap, flags, &bp);
if (error && error != -ENOENT)
goto out_put_perag;
@@ -584,7 +557,7 @@ xfs_buf_get_map(
goto out_put_perag;
/* xfs_buf_find_insert() consumes the perag reference. */
error = xfs_buf_find_insert(btp, bch, pag, &cmap, map, nmaps,
error = xfs_buf_find_insert(btp, pag, &cmap, map, nmaps,
flags, &bp);
if (error)
return error;
@@ -848,11 +821,8 @@ xfs_buf_destroy(
ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
if (!xfs_buf_is_uncached(bp)) {
struct xfs_buf_cache *bch =
xfs_buftarg_buf_cache(bp->b_target, bp->b_pag);
rhashtable_remove_fast(&bch->bc_hash, &bp->b_rhash_head,
xfs_buf_hash_params);
rhashtable_remove_fast(&bp->b_target->bt_hash,
&bp->b_rhash_head, xfs_buf_hash_params);
if (bp->b_pag)
xfs_perag_put(bp->b_pag);
@@ -1618,6 +1588,7 @@ xfs_destroy_buftarg(
ASSERT(percpu_counter_sum(&btp->bt_readahead_count) == 0);
percpu_counter_destroy(&btp->bt_readahead_count);
list_lru_destroy(&btp->bt_lru);
rhashtable_destroy(&btp->bt_hash);
}
void
@@ -1712,8 +1683,10 @@ xfs_init_buftarg(
ratelimit_state_init(&btp->bt_ioerror_rl, 30 * HZ,
DEFAULT_RATELIMIT_BURST);
if (list_lru_init(&btp->bt_lru))
if (rhashtable_init(&btp->bt_hash, &xfs_buf_hash_params))
return -ENOMEM;
if (list_lru_init(&btp->bt_lru))
goto out_destroy_hash;
if (percpu_counter_init(&btp->bt_readahead_count, 0, GFP_KERNEL))
goto out_destroy_lru;
@@ -1731,6 +1704,8 @@ xfs_init_buftarg(
percpu_counter_destroy(&btp->bt_readahead_count);
out_destroy_lru:
list_lru_destroy(&btp->bt_lru);
out_destroy_hash:
rhashtable_destroy(&btp->bt_hash);
return -ENOMEM;
}

10
fs/xfs/xfs_buf.h
View File

@@ -69,13 +69,6 @@ typedef unsigned int xfs_buf_flags_t;
{ XBF_INCORE, "INCORE" }, \
{ XBF_TRYLOCK, "TRYLOCK" }
struct xfs_buf_cache {
struct rhashtable bc_hash;
};
int xfs_buf_cache_init(struct xfs_buf_cache *bch);
void xfs_buf_cache_destroy(struct xfs_buf_cache *bch);
/*
* The xfs_buftarg contains 2 notions of "sector size" -
*
@@ -113,8 +106,7 @@ struct xfs_buftarg {
unsigned int bt_awu_min;
unsigned int bt_awu_max;
/* built-in cache, if we're not using the perag one */
struct xfs_buf_cache bt_cache[];
struct rhashtable bt_hash;
};
struct xfs_buf_map {

11
fs/xfs/xfs_buf_mem.c
View File

@@ -58,7 +58,7 @@ xmbuf_alloc(
struct xfs_buftarg *btp;
int error;
btp = kzalloc_flex(*btp, bt_cache, 1);
btp = kzalloc_obj(*btp);
if (!btp)
return -ENOMEM;
@@ -81,10 +81,6 @@ xmbuf_alloc(
/* ensure all writes are below EOF to avoid pagecache zeroing */
i_size_write(inode, inode->i_sb->s_maxbytes);
error = xfs_buf_cache_init(btp->bt_cache);
if (error)
goto out_file;
/* Initialize buffer target */
btp->bt_mount = mp;
btp->bt_dev = (dev_t)-1U;
@@ -95,15 +91,13 @@ xmbuf_alloc(
error = xfs_init_buftarg(btp, XMBUF_BLOCKSIZE, descr);
if (error)
goto out_bcache;
goto out_file;
trace_xmbuf_create(btp);
*btpp = btp;
return 0;
out_bcache:
xfs_buf_cache_destroy(btp->bt_cache);
out_file:
fput(file);
out_free_btp:
@@ -122,7 +116,6 @@ xmbuf_free(
trace_xmbuf_free(btp);
xfs_destroy_buftarg(btp);
xfs_buf_cache_destroy(btp->bt_cache);
fput(btp->bt_file);
kfree(btp);
}