On Mon 13-06-11 16:09:27, Jan Kara wrote:
> jbd2_journal_remove_journal_head() can oops when trying to access
> journal_head returned by bh2jh(). This is caused for example by the
> following race:
> TASK1 TASK2
> jbd2_journal_commit_transaction()
> ...
> processing t_forget list
> __jbd2_journal_refile_buffer(jh);
> if (!jh->b_transaction) {
> jbd_unlock_bh_state(bh);
> jbd2_journal_try_to_free_buffers()
> jbd2_journal_grab_journal_head(bh)
> jbd_lock_bh_state(bh)
> __journal_try_to_free_buffer()
> jbd2_journal_put_journal_head(jh)
> jbd2_journal_remove_journal_head(bh);
>
> jbd2_journal_put_journal_head() in TASK2 sees that b_jcount == 0 and buffer
> is not part of any transaction and thus frees journal_head before TASK1 gets
> to doing so. Note that even buffer_head can be released by
> try_to_free_buffers() after jbd2_journal_put_journal_head() which adds even
> larger opportunity for oops (but I didn't see this happen in reality).
>
> Fix the problem by making transactions hold their own journal_head reference
> (in b_jcount). That way we don't have to remove journal_head explicitely via
> jbd2_journal_remove_journal_head() and instead just remove journal_head when
> b_jcount drops to zero. The result of this is that
> [__]jbd2_journal_refile_buffer(), [__]jbd2_journal_unfile_buffer(), and
> __jdb2_journal_remove_checkpoint() can free journal_head which needs
> modification of a few callers. Also we have to be careful because once
> journal_head is removed, buffer_head might be freed as well. So we have to get
> our own buffer_head reference where it matters.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Ted, have you picked up updated version of this patch?
Honza
> ---
> fs/jbd2/checkpoint.c | 25 +++++++------
> fs/jbd2/commit.c | 33 ++++++++++-------
> fs/jbd2/journal.c | 91 +++++++++++++++---------------------------------
> fs/jbd2/transaction.c | 67 +++++++++++++++++++-----------------
> include/linux/jbd2.h | 2 -
> 5 files changed, 97 insertions(+), 121 deletions(-)
>
> I've fixed up two comments in the patch. Otherwise the patch is unchanged.
>
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 3436d53..b14a53d 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -97,10 +97,14 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
>
> if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
> !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
> + /*
> + * Get our reference so that bh cannot be freed before
> + * we unlock it
> + */
> + get_bh(bh);
> JBUFFER_TRACE(jh, "remove from checkpoint list");
> ret = __jbd2_journal_remove_checkpoint(jh) + 1;
> jbd_unlock_bh_state(bh);
> - jbd2_journal_remove_journal_head(bh);
> BUFFER_TRACE(bh, "release");
> __brelse(bh);
> } else {
> @@ -223,8 +227,8 @@ restart:
> spin_lock(&journal->j_list_lock);
> goto restart;
> }
> + get_bh(bh);
> if (buffer_locked(bh)) {
> - atomic_inc(&bh->b_count);
> spin_unlock(&journal->j_list_lock);
> jbd_unlock_bh_state(bh);
> wait_on_buffer(bh);
> @@ -243,7 +247,6 @@ restart:
> */
> released = __jbd2_journal_remove_checkpoint(jh);
> jbd_unlock_bh_state(bh);
> - jbd2_journal_remove_journal_head(bh);
> __brelse(bh);
> }
>
> @@ -284,7 +287,7 @@ static int __process_buffer(journal_t *journal, struct journal_head *jh,
> int ret = 0;
>
> if (buffer_locked(bh)) {
> - atomic_inc(&bh->b_count);
> + get_bh(bh);
> spin_unlock(&journal->j_list_lock);
> jbd_unlock_bh_state(bh);
> wait_on_buffer(bh);
> @@ -316,12 +319,12 @@ static int __process_buffer(journal_t *journal, struct journal_head *jh,
> ret = 1;
> if (unlikely(buffer_write_io_error(bh)))
> ret = -EIO;
> + get_bh(bh);
> J_ASSERT_JH(jh, !buffer_jbddirty(bh));
> BUFFER_TRACE(bh, "remove from checkpoint");
> __jbd2_journal_remove_checkpoint(jh);
> spin_unlock(&journal->j_list_lock);
> jbd_unlock_bh_state(bh);
> - jbd2_journal_remove_journal_head(bh);
> __brelse(bh);
> } else {
> /*
> @@ -663,8 +666,8 @@ out:
> * checkpoint lists.
> *
> * The function returns 1 if it frees the transaction, 0 otherwise.
> + * The function can free jh and bh.
> *
> - * This function is called with the journal locked.
> * This function is called with j_list_lock held.
> * This function is called with jbd_lock_bh_state(jh2bh(jh))
> */
> @@ -684,13 +687,14 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
> }
> journal = transaction->t_journal;
>
> + JBUFFER_TRACE(jh, "removing from transaction");
> __buffer_unlink(jh);
> jh->b_cp_transaction = NULL;
> + jbd2_journal_put_journal_head(jh);
>
> if (transaction->t_checkpoint_list != NULL ||
> transaction->t_checkpoint_io_list != NULL)
> goto out;
> - JBUFFER_TRACE(jh, "transaction has no more buffers");
>
> /*
> * There is one special case to worry about: if we have just pulled the
> @@ -701,10 +705,8 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
> * The locking here around t_state is a bit sleazy.
> * See the comment at the end of jbd2_journal_commit_transaction().
> */
> - if (transaction->t_state != T_FINISHED) {
> - JBUFFER_TRACE(jh, "belongs to running/committing transaction");
> + if (transaction->t_state != T_FINISHED)
> goto out;
> - }
>
> /* OK, that was the last buffer for the transaction: we can now
> safely remove this transaction from the log */
> @@ -723,7 +725,6 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
> wake_up(&journal->j_wait_logspace);
> ret = 1;
> out:
> - JBUFFER_TRACE(jh, "exit");
> return ret;
> }
>
> @@ -742,6 +743,8 @@ void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
> J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
> J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
>
> + /* Get reference for checkpointing transaction */
> + jbd2_journal_grab_journal_head(jh2bh(jh));
> jh->b_cp_transaction = transaction;
>
> if (!transaction->t_checkpoint_list) {
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 6dd6515..4b2f482 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -856,10 +856,16 @@ restart_loop:
> while (commit_transaction->t_forget) {
> transaction_t *cp_transaction;
> struct buffer_head *bh;
> + int try_to_free = 0;
>
> jh = commit_transaction->t_forget;
> spin_unlock(&journal->j_list_lock);
> bh = jh2bh(jh);
> + /*
> + * Get a reference so that bh cannot be freed before we are
> + * done with it.
> + */
> + get_bh(bh);
> jbd_lock_bh_state(bh);
> J_ASSERT_JH(jh, jh->b_transaction == commit_transaction);
>
> @@ -922,28 +928,27 @@ restart_loop:
> __jbd2_journal_insert_checkpoint(jh, commit_transaction);
> if (is_journal_aborted(journal))
> clear_buffer_jbddirty(bh);
> - JBUFFER_TRACE(jh, "refile for checkpoint writeback");
> - __jbd2_journal_refile_buffer(jh);
> - jbd_unlock_bh_state(bh);
> } else {
> J_ASSERT_BH(bh, !buffer_dirty(bh));
> - /* The buffer on BJ_Forget list and not jbddirty means
> + /*
> + * The buffer on BJ_Forget list and not jbddirty means
> * it has been freed by this transaction and hence it
> * could not have been reallocated until this
> * transaction has committed. *BUT* it could be
> * reallocated once we have written all the data to
> * disk and before we process the buffer on BJ_Forget
> - * list. */
> - JBUFFER_TRACE(jh, "refile or unfile freed buffer");
> - __jbd2_journal_refile_buffer(jh);
> - if (!jh->b_transaction) {
> - jbd_unlock_bh_state(bh);
> - /* needs a brelse */
> - jbd2_journal_remove_journal_head(bh);
> - release_buffer_page(bh);
> - } else
> - jbd_unlock_bh_state(bh);
> + * list.
> + */
> + if (!jh->b_next_transaction)
> + try_to_free = 1;
> }
> + JBUFFER_TRACE(jh, "refile or unfile buffer");
> + __jbd2_journal_refile_buffer(jh);
> + jbd_unlock_bh_state(bh);
> + if (try_to_free)
> + release_buffer_page(bh); /* Drops bh reference */
> + else
> + __brelse(bh);
> cond_resched_lock(&journal->j_list_lock);
> }
> spin_unlock(&journal->j_list_lock);
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 728f7d3..3fd6fec 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -2079,10 +2079,9 @@ static void journal_free_journal_head(struct journal_head *jh)
> * When a buffer has its BH_JBD bit set it is immune from being released by
> * core kernel code, mainly via ->b_count.
> *
> - * A journal_head may be detached from its buffer_head when the journal_head's
> - * b_transaction, b_cp_transaction and b_next_transaction pointers are NULL.
> - * Various places in JBD call jbd2_journal_remove_journal_head() to indicate that the
> - * journal_head can be dropped if needed.
> + * A journal_head is detached from its buffer_head when the journal_head's
> + * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
> + * transaction (b_cp_transaction) hold their references to b_jcount.
> *
> * Various places in the kernel want to attach a journal_head to a buffer_head
> * _before_ attaching the journal_head to a transaction. To protect the
> @@ -2095,17 +2094,16 @@ static void journal_free_journal_head(struct journal_head *jh)
> * (Attach a journal_head if needed. Increments b_jcount)
> * struct journal_head *jh = jbd2_journal_add_journal_head(bh);
> * ...
> + * (Get another reference for transaction)
> + * jbd2_journal_grab_journal_head(bh);
> * jh->b_transaction = xxx;
> + * (Put original reference)
> * jbd2_journal_put_journal_head(jh);
> - *
> - * Now, the journal_head's b_jcount is zero, but it is safe from being released
> - * because it has a non-zero b_transaction.
> */
>
> /*
> * Give a buffer_head a journal_head.
> *
> - * Doesn't need the journal lock.
> * May sleep.
> */
> struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh)
> @@ -2169,61 +2167,29 @@ static void __journal_remove_journal_head(struct buffer_head *bh)
> struct journal_head *jh = bh2jh(bh);
>
> J_ASSERT_JH(jh, jh->b_jcount >= 0);
> -
> - get_bh(bh);
> - if (jh->b_jcount == 0) {
> - if (jh->b_transaction == NULL &&
> - jh->b_next_transaction == NULL &&
> - jh->b_cp_transaction == NULL) {
> - J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
> - J_ASSERT_BH(bh, buffer_jbd(bh));
> - J_ASSERT_BH(bh, jh2bh(jh) == bh);
> - BUFFER_TRACE(bh, "remove journal_head");
> - if (jh->b_frozen_data) {
> - printk(KERN_WARNING "%s: freeing "
> - "b_frozen_data\n",
> - __func__);
> - jbd2_free(jh->b_frozen_data, bh->b_size);
> - }
> - if (jh->b_committed_data) {
> - printk(KERN_WARNING "%s: freeing "
> - "b_committed_data\n",
> - __func__);
> - jbd2_free(jh->b_committed_data, bh->b_size);
> - }
> - bh->b_private = NULL;
> - jh->b_bh = NULL; /* debug, really */
> - clear_buffer_jbd(bh);
> - __brelse(bh);
> - journal_free_journal_head(jh);
> - } else {
> - BUFFER_TRACE(bh, "journal_head was locked");
> - }
> + J_ASSERT_JH(jh, jh->b_transaction == NULL);
> + J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
> + J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
> + J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
> + J_ASSERT_BH(bh, buffer_jbd(bh));
> + J_ASSERT_BH(bh, jh2bh(jh) == bh);
> + BUFFER_TRACE(bh, "remove journal_head");
> + if (jh->b_frozen_data) {
> + printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
> + jbd2_free(jh->b_frozen_data, bh->b_size);
> }
> + if (jh->b_committed_data) {
> + printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
> + jbd2_free(jh->b_committed_data, bh->b_size);
> + }
> + bh->b_private = NULL;
> + jh->b_bh = NULL; /* debug, really */
> + clear_buffer_jbd(bh);
> + journal_free_journal_head(jh);
> }
>
> /*
> - * jbd2_journal_remove_journal_head(): if the buffer isn't attached to a transaction
> - * and has a zero b_jcount then remove and release its journal_head. If we did
> - * see that the buffer is not used by any transaction we also "logically"
> - * decrement ->b_count.
> - *
> - * We in fact take an additional increment on ->b_count as a convenience,
> - * because the caller usually wants to do additional things with the bh
> - * after calling here.
> - * The caller of jbd2_journal_remove_journal_head() *must* run __brelse(bh) at some
> - * time. Once the caller has run __brelse(), the buffer is eligible for
> - * reaping by try_to_free_buffers().
> - */
> -void jbd2_journal_remove_journal_head(struct buffer_head *bh)
> -{
> - jbd_lock_bh_journal_head(bh);
> - __journal_remove_journal_head(bh);
> - jbd_unlock_bh_journal_head(bh);
> -}
> -
> -/*
> - * Drop a reference on the passed journal_head. If it fell to zero then try to
> + * Drop a reference on the passed journal_head. If it fell to zero then
> * release the journal_head from the buffer_head.
> */
> void jbd2_journal_put_journal_head(struct journal_head *jh)
> @@ -2233,11 +2199,12 @@ void jbd2_journal_put_journal_head(struct journal_head *jh)
> jbd_lock_bh_journal_head(bh);
> J_ASSERT_JH(jh, jh->b_jcount > 0);
> --jh->b_jcount;
> - if (!jh->b_jcount && !jh->b_transaction) {
> + if (!jh->b_jcount) {
> __journal_remove_journal_head(bh);
> + jbd_unlock_bh_journal_head(bh);
> __brelse(bh);
> - }
> - jbd_unlock_bh_journal_head(bh);
> + } else
> + jbd_unlock_bh_journal_head(bh);
> }
>
> /*
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 49646cc..5a3176d 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -30,6 +30,7 @@
> #include <linux/module.h>
>
> static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
> +static void __jbd2_journal_unfile_buffer(struct journal_head *jh);
>
> /*
> * jbd2_get_transaction: obtain a new transaction_t object.
> @@ -764,7 +765,6 @@ repeat:
> if (!jh->b_transaction) {
> JBUFFER_TRACE(jh, "no transaction");
> J_ASSERT_JH(jh, !jh->b_next_transaction);
> - jh->b_transaction = transaction;
> JBUFFER_TRACE(jh, "file as BJ_Reserved");
> spin_lock(&journal->j_list_lock);
> __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
> @@ -896,8 +896,6 @@ int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
> * committed and so it's safe to clear the dirty bit.
> */
> clear_buffer_dirty(jh2bh(jh));
> - jh->b_transaction = transaction;
> -
> /* first access by this transaction */
> jh->b_modified = 0;
>
> @@ -1232,8 +1230,6 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
> __jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
> } else {
> __jbd2_journal_unfile_buffer(jh);
> - jbd2_journal_remove_journal_head(bh);
> - __brelse(bh);
> if (!buffer_jbd(bh)) {
> spin_unlock(&journal->j_list_lock);
> jbd_unlock_bh_state(bh);
> @@ -1555,19 +1551,32 @@ void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
> mark_buffer_dirty(bh); /* Expose it to the VM */
> }
>
> -void __jbd2_journal_unfile_buffer(struct journal_head *jh)
> +/*
> + * Remove buffer from all transactions.
> + *
> + * Called with bh_state lock and j_list_lock
> + *
> + * jh and bh may be already freed when this function returns.
> + */
> +static void __jbd2_journal_unfile_buffer(struct journal_head *jh)
> {
> __jbd2_journal_temp_unlink_buffer(jh);
> jh->b_transaction = NULL;
> + jbd2_journal_put_journal_head(jh);
> }
>
> void jbd2_journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
> {
> - jbd_lock_bh_state(jh2bh(jh));
> + struct buffer_head *bh = jh2bh(jh);
> +
> + /* Get reference so that buffer cannot be freed before we unlock it */
> + get_bh(bh);
> + jbd_lock_bh_state(bh);
> spin_lock(&journal->j_list_lock);
> __jbd2_journal_unfile_buffer(jh);
> spin_unlock(&journal->j_list_lock);
> - jbd_unlock_bh_state(jh2bh(jh));
> + jbd_unlock_bh_state(bh);
> + __brelse(bh);
> }
>
> /*
> @@ -1594,8 +1603,6 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
> if (jh->b_jlist == BJ_None) {
> JBUFFER_TRACE(jh, "remove from checkpoint list");
> __jbd2_journal_remove_checkpoint(jh);
> - jbd2_journal_remove_journal_head(bh);
> - __brelse(bh);
> }
> }
> spin_unlock(&journal->j_list_lock);
> @@ -1658,7 +1665,6 @@ int jbd2_journal_try_to_free_buffers(journal_t *journal,
> /*
> * We take our own ref against the journal_head here to avoid
> * having to add tons of locking around each instance of
> - * jbd2_journal_remove_journal_head() and
> * jbd2_journal_put_journal_head().
> */
> jh = jbd2_journal_grab_journal_head(bh);
> @@ -1696,10 +1702,9 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
> int may_free = 1;
> struct buffer_head *bh = jh2bh(jh);
>
> - __jbd2_journal_unfile_buffer(jh);
> -
> if (jh->b_cp_transaction) {
> JBUFFER_TRACE(jh, "on running+cp transaction");
> + __jbd2_journal_temp_unlink_buffer(jh);
> /*
> * We don't want to write the buffer anymore, clear the
> * bit so that we don't confuse checks in
> @@ -1710,8 +1715,7 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
> may_free = 0;
> } else {
> JBUFFER_TRACE(jh, "on running transaction");
> - jbd2_journal_remove_journal_head(bh);
> - __brelse(bh);
> + __jbd2_journal_unfile_buffer(jh);
> }
> return may_free;
> }
> @@ -1989,6 +1993,8 @@ void __jbd2_journal_file_buffer(struct journal_head *jh,
>
> if (jh->b_transaction)
> __jbd2_journal_temp_unlink_buffer(jh);
> + else
> + jbd2_journal_grab_journal_head(bh);
> jh->b_transaction = transaction;
>
> switch (jlist) {
> @@ -2040,9 +2046,10 @@ void jbd2_journal_file_buffer(struct journal_head *jh,
> * already started to be used by a subsequent transaction, refile the
> * buffer on that transaction's metadata list.
> *
> - * Called under journal->j_list_lock
> - *
> + * Called under j_list_lock
> * Called under jbd_lock_bh_state(jh2bh(jh))
> + *
> + * jh and bh may be already free when this function returns
> */
> void __jbd2_journal_refile_buffer(struct journal_head *jh)
> {
> @@ -2066,6 +2073,11 @@ void __jbd2_journal_refile_buffer(struct journal_head *jh)
>
> was_dirty = test_clear_buffer_jbddirty(bh);
> __jbd2_journal_temp_unlink_buffer(jh);
> + /*
> + * We set b_transaction here because b_next_transaction will inherit
> + * our jh reference and thus __jbd2_journal_file_buffer() must not
> + * take a new one.
> + */
> jh->b_transaction = jh->b_next_transaction;
> jh->b_next_transaction = NULL;
> if (buffer_freed(bh))
> @@ -2082,30 +2094,21 @@ void __jbd2_journal_refile_buffer(struct journal_head *jh)
> }
>
> /*
> - * For the unlocked version of this call, also make sure that any
> - * hanging journal_head is cleaned up if necessary.
> - *
> - * __jbd2_journal_refile_buffer is usually called as part of a single locked
> - * operation on a buffer_head, in which the caller is probably going to
> - * be hooking the journal_head onto other lists. In that case it is up
> - * to the caller to remove the journal_head if necessary. For the
> - * unlocked jbd2_journal_refile_buffer call, the caller isn't going to be
> - * doing anything else to the buffer so we need to do the cleanup
> - * ourselves to avoid a jh leak.
> - *
> - * *** The journal_head may be freed by this call! ***
> + * __jbd2_journal_refile_buffer() with necessary locking added. We take our
> + * bh reference so that we can safely unlock bh.
> + *
> + * The jh and bh may be freed by this call.
> */
> void jbd2_journal_refile_buffer(journal_t *journal, struct journal_head *jh)
> {
> struct buffer_head *bh = jh2bh(jh);
>
> + /* Get reference so that buffer cannot be freed before we unlock it */
> + get_bh(bh);
> jbd_lock_bh_state(bh);
> spin_lock(&journal->j_list_lock);
> -
> __jbd2_journal_refile_buffer(jh);
> jbd_unlock_bh_state(bh);
> - jbd2_journal_remove_journal_head(bh);
> -
> spin_unlock(&journal->j_list_lock);
> __brelse(bh);
> }
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 309cc49..54eb7f9 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1027,7 +1027,6 @@ struct journal_s
>
> /* Filing buffers */
> extern void jbd2_journal_unfile_buffer(journal_t *, struct journal_head *);
> -extern void __jbd2_journal_unfile_buffer(struct journal_head *);
> extern void __jbd2_journal_refile_buffer(struct journal_head *);
> extern void jbd2_journal_refile_buffer(journal_t *, struct journal_head *);
> extern void __jbd2_journal_file_buffer(struct journal_head *, transaction_t *, int);
> @@ -1168,7 +1167,6 @@ extern void jbd2_journal_release_jbd_inode(journal_t *journal, struct jbd2_in
> */
> struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh);
> struct journal_head *jbd2_journal_grab_journal_head(struct buffer_head *bh);
> -void jbd2_journal_remove_journal_head(struct buffer_head *bh);
> void jbd2_journal_put_journal_head(struct journal_head *jh);
>
> /*
> --
> 1.7.1
>
> --
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--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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