On Mon 26-11-12 14:55:09, Herton Ronaldo Krzesinski wrote:
> 3.5.7u1 -stable review patch. If anyone has any objections, please let me
> know.
Note that this fix causes another problem which is fixed by
25389bb207987b5774182f763b9fb65ff08761c8 upstream.
Honza
>
> ------------------
>
> From: Jan Kara <[email protected]>
>
> commit 09e05d4805e6c524c1af74e524e5d0528bb3fef3 upstream.
>
> ext3 users of data=journal mode with blocksize < pagesize were occasionally
> hitting assertion failure in journal_commit_transaction() checking whether the
> transaction has at least as many credits reserved as buffers attached. The
> core of the problem is that when a file gets truncated, buffers that still
> need
> checkpointing or that are attached to the committing transaction are left with
> buffer_mapped set. When this happens to buffers beyond i_size attached to a
> page stradding i_size, subsequent write extending the file will see these
> buffers and as they are mapped (but underlying blocks were freed) things go
> awry from here.
>
> The assertion failure just coincidentally (and in this case luckily as we
> would
> start corrupting filesystem) triggers due to journal_head not being properly
> cleaned up as well.
>
> Under some rare circumstances this bug could even hit data=ordered mode users.
> There the assertion won't trigger and we would end up corrupting the
> filesystem.
>
> We fix the problem by unmapping buffers if possible (in lots of cases we just
> need a buffer attached to a transaction as a place holder but it must not be
> written out anyway). And in one case, we just have to bite the bullet and wait
> for transaction commit to finish.
>
> Reviewed-by: Josef Bacik <[email protected]>
> Signed-off-by: Jan Kara <[email protected]>
> Signed-off-by: Herton Ronaldo Krzesinski <[email protected]>
> ---
> fs/jbd/commit.c | 45 ++++++++++++++++++++++++++---------
> fs/jbd/transaction.c | 64
> ++++++++++++++++++++++++++++++++++----------------
> 2 files changed, 78 insertions(+), 31 deletions(-)
>
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 52c15c7..86b39b1 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -86,7 +86,12 @@ nope:
> static void release_data_buffer(struct buffer_head *bh)
> {
> if (buffer_freed(bh)) {
> + WARN_ON_ONCE(buffer_dirty(bh));
> clear_buffer_freed(bh);
> + clear_buffer_mapped(bh);
> + clear_buffer_new(bh);
> + clear_buffer_req(bh);
> + bh->b_bdev = NULL;
> release_buffer_page(bh);
> } else
> put_bh(bh);
> @@ -866,17 +871,35 @@ restart_loop:
> * there's no point in keeping a checkpoint record for
> * it. */
>
> - /* A buffer which has been freed while still being
> - * journaled by a previous transaction may end up still
> - * being dirty here, but we want to avoid writing back
> - * that buffer in the future after the "add to orphan"
> - * operation been committed, That's not only a performance
> - * gain, it also stops aliasing problems if the buffer is
> - * left behind for writeback and gets reallocated for another
> - * use in a different page. */
> - if (buffer_freed(bh) && !jh->b_next_transaction) {
> - clear_buffer_freed(bh);
> - clear_buffer_jbddirty(bh);
> + /*
> + * A buffer which has been freed while still being journaled by
> + * a previous transaction.
> + */
> + if (buffer_freed(bh)) {
> + /*
> + * If the running transaction is the one containing
> + * "add to orphan" operation (b_next_transaction !=
> + * NULL), we have to wait for that transaction to
> + * commit before we can really get rid of the buffer.
> + * So just clear b_modified to not confuse transaction
> + * credit accounting and refile the buffer to
> + * BJ_Forget of the running transaction. If the just
> + * committed transaction contains "add to orphan"
> + * operation, we can completely invalidate the buffer
> + * now. We are rather throughout in that since the
> + * buffer may be still accessible when blocksize <
> + * pagesize and it is attached to the last partial
> + * page.
> + */
> + jh->b_modified = 0;
> + if (!jh->b_next_transaction) {
> + clear_buffer_freed(bh);
> + clear_buffer_jbddirty(bh);
> + clear_buffer_mapped(bh);
> + clear_buffer_new(bh);
> + clear_buffer_req(bh);
> + bh->b_bdev = NULL;
> + }
> }
>
> if (buffer_jbddirty(bh)) {
> diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
> index febc10d..78b7f84 100644
> --- a/fs/jbd/transaction.c
> +++ b/fs/jbd/transaction.c
> @@ -1843,15 +1843,16 @@ static int __dispose_buffer(struct journal_head *jh,
> transaction_t *transaction)
> * We're outside-transaction here. Either or both of j_running_transaction
> * and j_committing_transaction may be NULL.
> */
> -static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh)
> +static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh,
> + int partial_page)
> {
> transaction_t *transaction;
> struct journal_head *jh;
> int may_free = 1;
> - int ret;
>
> BUFFER_TRACE(bh, "entry");
>
> +retry:
> /*
> * It is safe to proceed here without the j_list_lock because the
> * buffers cannot be stolen by try_to_free_buffers as long as we are
> @@ -1879,10 +1880,18 @@ static int journal_unmap_buffer(journal_t *journal,
> struct buffer_head *bh)
> * clear the buffer dirty bit at latest at the moment when the
> * transaction marking the buffer as freed in the filesystem
> * structures is committed because from that moment on the
> - * buffer can be reallocated and used by a different page.
> + * block can be reallocated and used by a different page.
> * Since the block hasn't been freed yet but the inode has
> * already been added to orphan list, it is safe for us to add
> * the buffer to BJ_Forget list of the newest transaction.
> + *
> + * Also we have to clear buffer_mapped flag of a truncated buffer
> + * because the buffer_head may be attached to the page straddling
> + * i_size (can happen only when blocksize < pagesize) and thus the
> + * buffer_head can be reused when the file is extended again. So we end
> + * up keeping around invalidated buffers attached to transactions'
> + * BJ_Forget list just to stop checkpointing code from cleaning up
> + * the transaction this buffer was modified in.
> */
> transaction = jh->b_transaction;
> if (transaction == NULL) {
> @@ -1909,13 +1918,9 @@ static int journal_unmap_buffer(journal_t *journal,
> struct buffer_head *bh)
> * committed, the buffer won't be needed any
> * longer. */
> JBUFFER_TRACE(jh, "checkpointed: add to BJ_Forget");
> - ret = __dispose_buffer(jh,
> + may_free = __dispose_buffer(jh,
> journal->j_running_transaction);
> - journal_put_journal_head(jh);
> - spin_unlock(&journal->j_list_lock);
> - jbd_unlock_bh_state(bh);
> - spin_unlock(&journal->j_state_lock);
> - return ret;
> + goto zap_buffer;
> } else {
> /* There is no currently-running transaction. So the
> * orphan record which we wrote for this file must have
> @@ -1923,13 +1928,9 @@ static int journal_unmap_buffer(journal_t *journal,
> struct buffer_head *bh)
> * the committing transaction, if it exists. */
> if (journal->j_committing_transaction) {
> JBUFFER_TRACE(jh, "give to committing trans");
> - ret = __dispose_buffer(jh,
> + may_free = __dispose_buffer(jh,
> journal->j_committing_transaction);
> - journal_put_journal_head(jh);
> - spin_unlock(&journal->j_list_lock);
> - jbd_unlock_bh_state(bh);
> - spin_unlock(&journal->j_state_lock);
> - return ret;
> + goto zap_buffer;
> } else {
> /* The orphan record's transaction has
> * committed. We can cleanse this buffer */
> @@ -1950,10 +1951,24 @@ static int journal_unmap_buffer(journal_t *journal,
> struct buffer_head *bh)
> }
> /*
> * The buffer is committing, we simply cannot touch
> - * it. So we just set j_next_transaction to the
> - * running transaction (if there is one) and mark
> - * buffer as freed so that commit code knows it should
> - * clear dirty bits when it is done with the buffer.
> + * it. If the page is straddling i_size we have to wait
> + * for commit and try again.
> + */
> + if (partial_page) {
> + tid_t tid = journal->j_committing_transaction->t_tid;
> +
> + journal_put_journal_head(jh);
> + spin_unlock(&journal->j_list_lock);
> + jbd_unlock_bh_state(bh);
> + spin_unlock(&journal->j_state_lock);
> + log_wait_commit(journal, tid);
> + goto retry;
> + }
> + /*
> + * OK, buffer won't be reachable after truncate. We just set
> + * j_next_transaction to the running transaction (if there is
> + * one) and mark buffer as freed so that commit code knows it
> + * should clear dirty bits when it is done with the buffer.
> */
> set_buffer_freed(bh);
> if (journal->j_running_transaction && buffer_jbddirty(bh))
> @@ -1976,6 +1991,14 @@ static int journal_unmap_buffer(journal_t *journal,
> struct buffer_head *bh)
> }
>
> zap_buffer:
> + /*
> + * This is tricky. Although the buffer is truncated, it may be reused
> + * if blocksize < pagesize and it is attached to the page straddling
> + * EOF. Since the buffer might have been added to BJ_Forget list of the
> + * running transaction, journal_get_write_access() won't clear
> + * b_modified and credit accounting gets confused. So clear b_modified
> + * here. */
> + jh->b_modified = 0;
> journal_put_journal_head(jh);
> zap_buffer_no_jh:
> spin_unlock(&journal->j_list_lock);
> @@ -2024,7 +2047,8 @@ void journal_invalidatepage(journal_t *journal,
> if (offset <= curr_off) {
> /* This block is wholly outside the truncation point */
> lock_buffer(bh);
> - may_free &= journal_unmap_buffer(journal, bh);
> + may_free &= journal_unmap_buffer(journal, bh,
> + offset > 0);
> unlock_buffer(bh);
> }
> curr_off = next_off;
> --
> 1.7.9.5
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
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