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Date: Mon, 19 May 2008 00:37:39 +0200
From: Jan Kara <jack@...e.cz>
To: Mingming Cao <cmm@...ibm.com>
Cc: akpm@...ux-foundation.org, Badari Pulavarty <pbadari@...ibm.com>,
linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] JBD: Fix DIO EIO error caused by race between free buffer and commit trasanction
Hi,
> This patch fixed a few races between direct IO and kjournald commit
> transaction. An unexpected EIO error gets returned to direct IO
> caller when it failed to free those data buffers. This could be
> reproduced easily with parallel direct write and buffered write to the
> same file
>
> More specific, those races could cause journal_try_to_free_buffers()
> fail to free the data buffers, when jbd is committing the transaction
> that has those data buffers on its t_syncdata_list or t_locked_list.
> journal_commit_transaction() still holds the reference to those
> buffers before data reach to disk and buffers are removed from the
> t_syncdata_list of t_locked_list. This prevent the concurrent
> journal_try_to_free_buffers() to free those buffers at the same time,
> but cause EIO error returns back to direct IO.
>
> With this patch, in case of direct IO and when try_to_free_buffers() failed,
> let's waiting for journal_commit_transaction() to finish
> flushing the current committing transaction's data buffers to disk,
> then try to free those buffers again.
If Andrew or Christoph wouldn't beat you for "inventive use" of
gfp_mask, I'm fine with the patch as well ;). You can add
Acked-by: Jan Kara <jack@...e.cz>
>
> Signed-off-by: Mingming Cao <cmm@...ibm.com>
> Reviewed-by: Badari Pulavarty <pbadari@...ibm.com>
> ---
> fs/jbd/transaction.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++--
> mm/truncate.c | 3 +-
> 2 files changed, 57 insertions(+), 3 deletions(-)
>
> Index: linux-2.6.26-rc2/fs/jbd/transaction.c
> ===================================================================
> --- linux-2.6.26-rc2.orig/fs/jbd/transaction.c 2008-05-16 11:51:02.000000000 -0700
> +++ linux-2.6.26-rc2/fs/jbd/transaction.c 2008-05-16 13:43:02.000000000 -0700
> @@ -1648,12 +1648,39 @@ out:
> return;
> }
>
> +/*
> + * journal_try_to_free_buffers() could race with journal_commit_transaction()
> + * The later might still hold the reference count to the buffers when inspecting
> + * them on t_syncdata_list or t_locked_list.
> + *
> + * Journal_try_to_free_buffers() will call this function to
> + * wait for the current transaction to finish syncing data buffers, before
> + * try to free that buffer.
> + *
> + * Called with journal->j_state_lock hold.
> + */
> +static void journal_wait_for_transaction_sync_data(journal_t *journal)
> +{
> + transaction_t *transaction = NULL;
> + tid_t tid;
> +
> + transaction = journal->j_committing_transaction;
> +
> + if (!transaction)
> + return;
> +
> + tid = transaction->t_tid;
> + spin_unlock(&journal->j_state_lock);
> + log_wait_commit(journal, tid);
> + spin_lock(&journal->j_state_lock);
> +}
>
> /**
> * int journal_try_to_free_buffers() - try to free page buffers.
> * @journal: journal for operation
> * @page: to try and free
> - * @unused_gfp_mask: unused
> + * @gfp_mask: unused for allocation purpose. Here is used
> + * as a flag to tell if direct IO is attemping to free buffers.
> *
> *
> * For all the buffers on this page,
> @@ -1682,9 +1709,11 @@ out:
> * journal_try_to_free_buffer() is changing its state. But that
> * cannot happen because we never reallocate freed data as metadata
> * while the data is part of a transaction. Yes?
> + *
> + * Return 0 on failure, 1 on success
> */
> int journal_try_to_free_buffers(journal_t *journal,
> - struct page *page, gfp_t unused_gfp_mask)
> + struct page *page, gfp_t gfp_mask)
> {
> struct buffer_head *head;
> struct buffer_head *bh;
> @@ -1713,7 +1742,31 @@ int journal_try_to_free_buffers(journal_
> if (buffer_jbd(bh))
> goto busy;
> } while ((bh = bh->b_this_page) != head);
> +
> ret = try_to_free_buffers(page);
> +
> + /*
> + * In the case of concurrent direct IO and buffered IO,
> + * There are a number of places where we
> + * could race with journal_commit_transaction(), the later still
> + * holds the reference to the buffers to free while processing them.
> + * try_to_free_buffers() failed to free those buffers,
> + * resulting in an unexpected EIO error
> + * returns back to the generic_file_direct_IO()
> + *
> + * So let's wait for the current transaction to finish flush of
> + * dirty data buffers before we try to free those buffers
> + * again. This wait is needed by direct IO code path only,
> + * gfp_mask __GFP_REPEAT is passed from the direct IO code
> + * path to flag if we need to wait and retry free buffers.
> + */
> + if (ret == 0 && gfp_mask & __GFP_REPEAT) {
> + spin_lock(&journal->j_state_lock);
> + journal_wait_for_transaction_sync_data(journal);
> + ret = try_to_free_buffers(page);
> + spin_unlock(&journal->j_state_lock);
> + }
> +
> busy:
> return ret;
> }
> Index: linux-2.6.26-rc2/mm/truncate.c
> ===================================================================
> --- linux-2.6.26-rc2.orig/mm/truncate.c 2008-05-16 11:51:02.000000000 -0700
> +++ linux-2.6.26-rc2/mm/truncate.c 2008-05-16 13:42:18.000000000 -0700
> @@ -346,7 +346,8 @@ invalidate_complete_page2(struct address
> if (page->mapping != mapping)
> return 0;
>
> - if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
> + if (PagePrivate(page) &&
> + !try_to_release_page(page,GFP_KERNEL|__GFP_REPEAT))
> return 0;
>
> write_lock_irq(&mapping->tree_lock);
>
>
> --
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Honza
--
Jan Kara <jack@...e.cz>
SuSE CR Labs
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