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authorDaeho Jeong <daeho.jeong@samsung.com>2016-04-25 23:22:35 -0400
committerTheodore Ts'o <tytso@mit.edu>2016-04-25 23:22:35 -0400
commitc8585c6fcaf2011de54c3592e80a634a2b9e1a7f (patch)
tree66b440a3e710ab4b63ae20200735a594bffb74cd
parent4c54659269ecb799133758330e7ea2a6fa4c65ca (diff)
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>
-rw-r--r--fs/ext4/ext4.h4
-rw-r--r--fs/ext4/inode.c15
-rw-r--r--fs/ext4/super.c4
-rw-r--r--kernel/locking/percpu-rwsem.c1
4 files changed, 21 insertions, 3 deletions
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cb00b1119ec9..ba5aecc07fbc 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -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)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 779ef4c11bc1..4d8ebbe00456 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -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,
- wbc);
+ 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 @@ retry:
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);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 304c712dbe12..20c5d52253b4 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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 @@ no_journal:
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;
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index f231e0bb311c..bec0b647f9cc 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -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