jbd2: preserve original nofs flag during journal restart

When a transaction starts, start_this_handle() saves current
PF_MEMALLOC_NOFS value so that it can be restored at journal stop time.
Journal restart is a special case that calls start_this_handle() without
stopping the transaction. start_this_handle() isn't aware that the
original value is already stored so it overwrites it with current value.

For instance, a call sequence like below leaves PF_MEMALLOC_NOFS flag set
at the end:

jbd2_journal_start()
jbd2__journal_restart()
jbd2_journal_stop()

Make jbd2__journal_restart() restore the original value before calling
start_this_handle().

Fixes: 81378da64de6 ("jbd2: mark the transaction context with the scope GFP_NOFS context")
Signed-off-by: Tahsin Erdogan <[e-mail]>
Signed-off-by: Theodore Ts'o <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>

fs/jbd2/transaction.c

···
 
 	rwsem_release(&journal->j_trans_commit_map, 1, _THIS_IP_);
 	handle->h_buffer_credits = nblocks;
+	/*
+	 * Restore the original nofs context because the journal restart
+	 * is basically the same thing as journal stop and start.
+	 * start_this_handle will start a new nofs context.
+	 */
+	memalloc_nofs_restore(handle->saved_alloc_context);
 	ret = start_this_handle(journal, handle, gfp_mask);
 	return ret;
 }