Commit 46bf2e9c authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcachefs: Fix excess transaction restarts in __bchfs_fallocate() 



drop_locks_do() should not be used in a fastpath without first trying
the do in nonblocking mode - the unlock and relock will cause excessive
transaction restarts and potentially livelocking with other threads that
are contending for the same locks.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 1a503904

fs/bcachefs/btree_iter.h

+5 −0
Original line number Diff line number Diff line
@@ -819,6 +819,11 @@ __bch2_btree_iter_peek_and_restart(struct btree_trans *trans, 
#define for_each_btree_key_continue_norestart(_iter, _flags, _k, _ret)	\

	for_each_btree_key_upto_continue_norestart(_iter, SPOS_MAX, _flags, _k, _ret)



/*

 * This should not be used in a fastpath, without first trying _do in

 * nonblocking mode - it will cause excessive transaction restarts and

 * potentially livelocking:

 */

#define drop_locks_do(_trans, _do)					\

({									\

	bch2_trans_unlock(_trans);					\

fs/bcachefs/fs-io-pagecache.c

+24 −13
Original line number Diff line number Diff line
@@ -309,39 +309,49 @@ void bch2_mark_pagecache_unallocated(struct bch_inode_info *inode, 
	}

}



void bch2_mark_pagecache_reserved(struct bch_inode_info *inode,

				  u64 start, u64 end)

int bch2_mark_pagecache_reserved(struct bch_inode_info *inode,

				 u64 *start, u64 end,

				 bool nonblocking)

{

	struct bch_fs *c = inode->v.i_sb->s_fs_info;

	pgoff_t index = start >> PAGE_SECTORS_SHIFT;

	pgoff_t index = *start >> PAGE_SECTORS_SHIFT;

	pgoff_t end_index = (end - 1) >> PAGE_SECTORS_SHIFT;

	struct folio_batch fbatch;

	s64 i_sectors_delta = 0;

	unsigned i, j;

	int ret = 0;



	if (end <= start)

		return;

	if (end <= *start)

		return 0;



	folio_batch_init(&fbatch);



	while (filemap_get_folios(inode->v.i_mapping,

				  &index, end_index, &fbatch)) {

		for (i = 0; i < folio_batch_count(&fbatch); i++) {

		for (unsigned i = 0; i < folio_batch_count(&fbatch); i++) {

			struct folio *folio = fbatch.folios[i];



			if (!nonblocking)

				folio_lock(folio);

			else if (!folio_trylock(folio)) {

				folio_batch_release(&fbatch);

				ret = -EAGAIN;

				break;

			}



			u64 folio_start = folio_sector(folio);

			u64 folio_end = folio_end_sector(folio);

			unsigned folio_offset = max(start, folio_start) - folio_start;

			unsigned folio_len = min(end, folio_end) - folio_offset - folio_start;

			struct bch_folio *s;



			BUG_ON(end <= folio_start);



			folio_lock(folio);

			s = bch2_folio(folio);

			*start = min(end, folio_end);



			struct bch_folio *s = bch2_folio(folio);

			if (s) {

				unsigned folio_offset = max(*start, folio_start) - folio_start;

				unsigned folio_len = min(end, folio_end) - folio_offset - folio_start;



				spin_lock(&s->lock);

				for (j = folio_offset; j < folio_offset + folio_len; j++) {

				for (unsigned j = folio_offset; j < folio_offset + folio_len; j++) {

					i_sectors_delta -= s->s[j].state == SECTOR_dirty;

					bch2_folio_sector_set(folio, s, j,

						folio_sector_reserve(s->s[j].state));
@@ -356,6 +366,7 @@ void bch2_mark_pagecache_reserved(struct bch_inode_info *inode, 
	}



	bch2_i_sectors_acct(c, inode, NULL, i_sectors_delta);

	return ret;

}



static inline unsigned sectors_to_reserve(struct bch_folio_sector *s,

fs/bcachefs/fs-io-pagecache.h

+1 −1
Original line number Diff line number Diff line
@@ -143,7 +143,7 @@ int bch2_folio_set(struct bch_fs *, subvol_inum, struct folio **, unsigned); 
void bch2_bio_page_state_set(struct bio *, struct bkey_s_c);



void bch2_mark_pagecache_unallocated(struct bch_inode_info *, u64, u64);

void bch2_mark_pagecache_reserved(struct bch_inode_info *, u64, u64);

int bch2_mark_pagecache_reserved(struct bch_inode_info *, u64 *, u64, bool);



int bch2_get_folio_disk_reservation(struct bch_fs *,

				struct bch_inode_info *,

fs/bcachefs/fs-io.c

+5 −2
Original line number Diff line number Diff line
@@ -675,8 +675,11 @@ static int __bchfs_fallocate(struct bch_inode_info *inode, int mode, 


		bch2_i_sectors_acct(c, inode, &quota_res, i_sectors_delta);



		if (bch2_mark_pagecache_reserved(inode, &hole_start,

						 iter.pos.offset, true))

			drop_locks_do(trans,

			(bch2_mark_pagecache_reserved(inode, hole_start, iter.pos.offset), 0));

				bch2_mark_pagecache_reserved(inode, &hole_start,

							     iter.pos.offset, false));

bkey_err:

		bch2_quota_reservation_put(c, inode, &quota_res);

		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))