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Commit c8585c6f authored by Daeho Jeong's avatar Daeho Jeong Committed by Theodore Ts'o
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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: default avatarDaeho Jeong <daeho.jeong@samsung.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
parent 4c546592

fs/ext4/ext4.h

+4 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include <linux/ratelimit.h>

#include <crypto/hash.h>

#include <linux/falloc.h>

#include <linux/percpu-rwsem.h>

#ifdef __KERNEL__

#include <linux/compat.h>

#endif
@@ -1508,6 +1509,9 @@ struct ext4_sb_info { 
	struct ratelimit_state s_err_ratelimit_state;

	struct ratelimit_state s_warning_ratelimit_state;

	struct ratelimit_state s_msg_ratelimit_state;



	/* Barrier between changing inodes' journal flags and writepages ops. */

	struct percpu_rw_semaphore s_journal_flag_rwsem;

};



static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)

fs/ext4/inode.c

+12 −3
Original line number Diff line number Diff line
@@ -2612,11 +2612,14 @@ static int ext4_writepages(struct address_space *mapping, 
	struct blk_plug plug;

	bool give_up_on_write = false;



	percpu_down_read(&sbi->s_journal_flag_rwsem);

	trace_ext4_writepages(inode, wbc);



	if (dax_mapping(mapping))

		return dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,

	if (dax_mapping(mapping)) {

		ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,

						  wbc);

		goto out_writepages;

	}



	/*

	 * No pages to write? This is mainly a kludge to avoid starting
@@ -2786,6 +2789,7 @@ static int ext4_writepages(struct address_space *mapping, 
out_writepages:

	trace_ext4_writepages_result(inode, wbc, ret,

				     nr_to_write - wbc->nr_to_write);

	percpu_up_read(&sbi->s_journal_flag_rwsem);

	return ret;

}
@@ -5436,6 +5440,7 @@ 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);



	/*

	 * We have to be very careful here: changing a data block's
@@ -5475,6 +5480,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) 
		}

	}



	percpu_down_write(&sbi->s_journal_flag_rwsem);

	jbd2_journal_lock_updates(journal);



	/*
@@ -5491,6 +5497,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val) 
		err = jbd2_journal_flush(journal);

		if (err < 0) {

			jbd2_journal_unlock_updates(journal);

			percpu_up_write(&sbi->s_journal_flag_rwsem);

			ext4_inode_resume_unlocked_dio(inode);

			return err;

		}
@@ -5499,6 +5506,8 @@ 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_journal_flag_rwsem);



	if (val)

		up_write(&EXT4_I(inode)->i_mmap_sem);

	ext4_inode_resume_unlocked_dio(inode);

fs/ext4/super.c

+4 −0
Original line number Diff line number Diff line
@@ -859,6 +859,7 @@ static void ext4_put_super(struct super_block *sb) 
	percpu_counter_destroy(&sbi->s_freeinodes_counter);

	percpu_counter_destroy(&sbi->s_dirs_counter);

	percpu_counter_destroy(&sbi->s_dirtyclusters_counter);

	percpu_free_rwsem(&sbi->s_journal_flag_rwsem);

	brelse(sbi->s_sbh);

#ifdef CONFIG_QUOTA

	for (i = 0; i < EXT4_MAXQUOTAS; i++)
@@ -3930,6 +3931,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) 
	if (!err)

		err = percpu_counter_init(&sbi->s_dirtyclusters_counter, 0,

					  GFP_KERNEL);

	if (!err)

		err = percpu_init_rwsem(&sbi->s_journal_flag_rwsem);



	if (err) {

		ext4_msg(sb, KERN_ERR, "insufficient memory");

		goto failed_mount6;

kernel/locking/percpu-rwsem.c

+1 −0
Original line number Diff line number Diff line
@@ -37,6 +37,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *brw) 
	free_percpu(brw->fast_read_ctr);

	brw->fast_read_ctr = NULL; /* catch use after free bugs */

}

EXPORT_SYMBOL_GPL(percpu_free_rwsem);



/*

 * This is the fast-path for down_read/up_read. If it succeeds we rely