The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 00d873c17e29cc32d90ca852b82685f1673acaa5 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023051530-pushcart-probably-f8cf@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

00d873c17e29 ("ext4: avoid deadlock in fs reclaim with page writeback") 1f1a55f0bf06 ("ext4: Commit transaction before writing back pages in data=journal mode") 3f079114bf52 ("ext4: Convert data=journal writeback to use ext4_writepages()") d8be7607de03 ("ext4: Move mpage_page_done() calls after error handling") eaf2ca10ca4b ("ext4: Move page unlocking out of mpage_submit_page()") f1496362e9d7 ("ext4: Don't unlock page in ext4_bio_write_page()") d585bdbeb79a ("fs: convert writepage_t callback to pass a folio") 50ead2537441 ("ext4: convert mpage_prepare_extent_to_map() to use filemap_get_folios_tag()") 0fff435f060c ("page-writeback: convert write_cache_pages() to use filemap_get_folios_tag()") c2ca7a59a419 ("mm: remove generic_writepages") 25a89826f270 ("ntfs3: remove ->writepage") d4428bad14dd ("ntfs3: stop using generic_writepages") 851f657a8642 ("Merge tag '6.2-rc-smb3-client-fixes-part1' of git://git.samba.org/sfrench/cifs-2.6")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 00d873c17e29cc32d90ca852b82685f1673acaa5 Mon Sep 17 00:00:00 2001 From: Jan Kara jack@suse.cz Date: Thu, 4 May 2023 14:47:23 +0200 Subject: [PATCH] ext4: avoid deadlock in fs reclaim with page writeback

Ext4 has a filesystem wide lock protecting ext4_writepages() calls to avoid races with switching of journalled data flag or inode format. This lock can however cause a deadlock like:

CPU0 CPU1

ext4_writepages() percpu_down_read(sbi->s_writepages_rwsem); ext4_change_inode_journal_flag() percpu_down_write(sbi->s_writepages_rwsem); - blocks, all readers block from now on ext4_do_writepages() ext4_init_io_end() kmem_cache_zalloc(io_end_cachep, GFP_KERNEL) fs_reclaim frees dentry... dentry_unlink_inode() iput() - last ref => iput_final() - inode dirty => write_inode_now()... ext4_writepages() tries to acquire sbi->s_writepages_rwsem and blocks forever

Make sure we cannot recurse into filesystem reclaim from writeback code to avoid the deadlock.

Reported-by: syzbot+6898da502aef574c5f8a@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/0000000000004c66b405fa108e27@google.com Fixes: c8585c6fcaf2 ("ext4: fix races between changing inode journal mode and ext4_writepages") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20230504124723.20205-1-jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 7e8f66ba17f4..6948d673bba2 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1684,6 +1684,30 @@ static inline struct ext4_inode_info *EXT4_I(struct inode *inode) return container_of(inode, struct ext4_inode_info, vfs_inode); }

+static inline int ext4_writepages_down_read(struct super_block *sb) +{ + percpu_down_read(&EXT4_SB(sb)->s_writepages_rwsem); + return memalloc_nofs_save(); +} + +static inline void ext4_writepages_up_read(struct super_block *sb, int ctx) +{ + memalloc_nofs_restore(ctx); + percpu_up_read(&EXT4_SB(sb)->s_writepages_rwsem); +} + +static inline int ext4_writepages_down_write(struct super_block *sb) +{ + percpu_down_write(&EXT4_SB(sb)->s_writepages_rwsem); + return memalloc_nofs_save(); +} + +static inline void ext4_writepages_up_write(struct super_block *sb, int ctx) +{ + memalloc_nofs_restore(ctx); + percpu_up_write(&EXT4_SB(sb)->s_writepages_rwsem); +} + static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino) { return ino == EXT4_ROOT_INO || diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 0d5ba922e411..3cb774d9e3f1 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2783,11 +2783,12 @@ static int ext4_writepages(struct address_space *mapping, .can_map = 1, }; int ret; + int alloc_ctx;

if (unlikely(ext4_forced_shutdown(EXT4_SB(sb)))) return -EIO;

- percpu_down_read(&EXT4_SB(sb)->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_read(sb); ret = ext4_do_writepages(&mpd); /* * For data=journal writeback we could have come across pages marked @@ -2796,7 +2797,7 @@ static int ext4_writepages(struct address_space *mapping, */ if (!ret && mpd.journalled_more_data) ret = ext4_do_writepages(&mpd); - percpu_up_read(&EXT4_SB(sb)->s_writepages_rwsem); + ext4_writepages_up_read(sb, alloc_ctx);

return ret; } @@ -2824,17 +2825,18 @@ static int ext4_dax_writepages(struct address_space *mapping, long nr_to_write = wbc->nr_to_write; struct inode *inode = mapping->host; struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb); + int alloc_ctx;

if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) return -EIO;

- percpu_down_read(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_read(inode->i_sb); trace_ext4_writepages(inode, wbc);

ret = dax_writeback_mapping_range(mapping, sbi->s_daxdev, wbc); trace_ext4_writepages_result(inode, wbc, ret, nr_to_write - wbc->nr_to_write); - percpu_up_read(&sbi->s_writepages_rwsem); + ext4_writepages_up_read(inode->i_sb, alloc_ctx); return ret; }

@@ -5928,7 +5930,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) journal_t *journal; handle_t *handle; int err; - struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + int alloc_ctx;

/* * We have to be very careful here: changing a data block's @@ -5966,7 +5968,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) } }

- percpu_down_write(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_write(inode->i_sb); jbd2_journal_lock_updates(journal);

/* @@ -5983,7 +5985,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) err = jbd2_journal_flush(journal, 0); if (err < 0) { jbd2_journal_unlock_updates(journal); - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return err; } ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA); @@ -5991,7 +5993,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) ext4_set_aops(inode);

jbd2_journal_unlock_updates(journal); - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx);

if (val) filemap_invalidate_unlock(inode->i_mapping); diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c index a19a9661646e..d98ac2af8199 100644 --- a/fs/ext4/migrate.c +++ b/fs/ext4/migrate.c @@ -408,7 +408,6 @@ static int free_ext_block(handle_t *handle, struct inode *inode)

int ext4_ext_migrate(struct inode *inode) { - struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); handle_t *handle; int retval = 0, i; __le32 *i_data; @@ -418,6 +417,7 @@ int ext4_ext_migrate(struct inode *inode) unsigned long max_entries; __u32 goal, tmp_csum_seed; uid_t owner[2]; + int alloc_ctx;

/* * If the filesystem does not support extents, or the inode @@ -434,7 +434,7 @@ int ext4_ext_migrate(struct inode *inode) */ return retval;

- percpu_down_write(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_write(inode->i_sb);

/* * Worst case we can touch the allocation bitmaps and a block @@ -586,7 +586,7 @@ int ext4_ext_migrate(struct inode *inode) unlock_new_inode(tmp_inode); iput(tmp_inode); out_unlock: - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return retval; }

@@ -605,6 +605,7 @@ int ext4_ind_migrate(struct inode *inode) ext4_fsblk_t blk; handle_t *handle; int ret, ret2 = 0; + int alloc_ctx;

if (!ext4_has_feature_extents(inode->i_sb) || (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) @@ -621,7 +622,7 @@ int ext4_ind_migrate(struct inode *inode) if (test_opt(inode->i_sb, DELALLOC)) ext4_alloc_da_blocks(inode);

- percpu_down_write(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_write(inode->i_sb);

handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1); if (IS_ERR(handle)) { @@ -665,6 +666,6 @@ int ext4_ind_migrate(struct inode *inode) ext4_journal_stop(handle); up_write(&EXT4_I(inode)->i_data_sem); out_unlock: - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return ret; }