ext4: fix races between changing inode journal mode and ext4_writepages
In ext4, there is a race condition between changing inode journal mode and ext4_writepages(). While ext4_writepages() is executed on a non-journalled mode inode, the inode's journal mode could be enabled by ioctl() and then, some pages dirtied after switching the journal mode will be still exposed to ext4_writepages() in non-journaled mode. To resolve this problem, we use fs-wide per-cpu rw semaphore by Jan Kara's suggestion because we don't want to waste ext4_inode_info's space for this extra rare case. Signed-off-by: Daeho Jeong <daeho.jeong@samsung.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jan Kara <jack@suse.cz>
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@ -33,6 +33,7 @@
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#include <linux/ratelimit.h>
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#include <crypto/hash.h>
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#include <linux/falloc.h>
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#include <linux/percpu-rwsem.h>
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#ifdef __KERNEL__
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#include <linux/compat.h>
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#endif
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@ -1508,6 +1509,9 @@ struct ext4_sb_info {
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struct ratelimit_state s_err_ratelimit_state;
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struct ratelimit_state s_warning_ratelimit_state;
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struct ratelimit_state s_msg_ratelimit_state;
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/* Barrier between changing inodes' journal flags and writepages ops. */
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struct percpu_rw_semaphore s_journal_flag_rwsem;
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};
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static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
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@ -2612,11 +2612,14 @@ static int ext4_writepages(struct address_space *mapping,
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struct blk_plug plug;
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bool give_up_on_write = false;
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percpu_down_read(&sbi->s_journal_flag_rwsem);
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trace_ext4_writepages(inode, wbc);
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if (dax_mapping(mapping))
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return dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,
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wbc);
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if (dax_mapping(mapping)) {
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ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,
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wbc);
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goto out_writepages;
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}
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/*
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* No pages to write? This is mainly a kludge to avoid starting
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@ -2786,6 +2789,7 @@ retry:
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out_writepages:
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trace_ext4_writepages_result(inode, wbc, ret,
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nr_to_write - wbc->nr_to_write);
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percpu_up_read(&sbi->s_journal_flag_rwsem);
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return ret;
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}
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@ -5436,6 +5440,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
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journal_t *journal;
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handle_t *handle;
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int err;
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struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
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/*
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* We have to be very careful here: changing a data block's
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@ -5475,6 +5480,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
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}
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}
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percpu_down_write(&sbi->s_journal_flag_rwsem);
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jbd2_journal_lock_updates(journal);
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/*
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@ -5491,6 +5497,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
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err = jbd2_journal_flush(journal);
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if (err < 0) {
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jbd2_journal_unlock_updates(journal);
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percpu_up_write(&sbi->s_journal_flag_rwsem);
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ext4_inode_resume_unlocked_dio(inode);
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return err;
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}
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@ -5499,6 +5506,8 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
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ext4_set_aops(inode);
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jbd2_journal_unlock_updates(journal);
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percpu_up_write(&sbi->s_journal_flag_rwsem);
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if (val)
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up_write(&EXT4_I(inode)->i_mmap_sem);
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ext4_inode_resume_unlocked_dio(inode);
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@ -859,6 +859,7 @@ static void ext4_put_super(struct super_block *sb)
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percpu_counter_destroy(&sbi->s_freeinodes_counter);
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percpu_counter_destroy(&sbi->s_dirs_counter);
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percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
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percpu_free_rwsem(&sbi->s_journal_flag_rwsem);
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brelse(sbi->s_sbh);
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#ifdef CONFIG_QUOTA
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for (i = 0; i < EXT4_MAXQUOTAS; i++)
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@ -3930,6 +3931,9 @@ no_journal:
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if (!err)
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err = percpu_counter_init(&sbi->s_dirtyclusters_counter, 0,
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GFP_KERNEL);
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if (!err)
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err = percpu_init_rwsem(&sbi->s_journal_flag_rwsem);
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if (err) {
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ext4_msg(sb, KERN_ERR, "insufficient memory");
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goto failed_mount6;
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@ -37,6 +37,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
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free_percpu(brw->fast_read_ctr);
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brw->fast_read_ctr = NULL; /* catch use after free bugs */
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}
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EXPORT_SYMBOL_GPL(percpu_free_rwsem);
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/*
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* This is the fast-path for down_read/up_read. If it succeeds we rely
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