Date:	Thu, 30 Nov 2006 04:56:31 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	akpm@...l.org
cc:	mm-commits@...r.kernel.org, cmm@...ibm.com,
	linux-ext4@...r.kernel.org
Subject: Re: + ext3-balloc-fix-_with_rsv-freeze.patch added to -mm tree

On Wed, 29 Nov 2006, akpm@...l.org wrote:
> 
> The patch titled
>      ext3 balloc: fix _with_rsv freeze
> has been added to the -mm tree.  Its filename is
>      ext3-balloc-fix-_with_rsv-freeze.patch
> 
> See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
> out what to do about this
> 
> ------------------------------------------------------
> Subject: ext3 balloc: fix _with_rsv freeze
> From: Hugh Dickins <hugh@...itas.com>
> 
> After several days of testing ext3 with reservations, it got caught inside
> ext3_try_to_allocate_with_rsv: alloc_new_reservation repeatedly succeeding
> on the window [12cff,12d0e], ext3_try_to_allocate repeatedly failing to
> find the free block guaranteed to be included (unless there's contention).

Thanks a lot for changing the comments on these twelve, substituting
ext3 or ext4 for ext2 where appropriate: I much prefer these.

But in the case of this ext3-balloc-fix-_with_rsv-freeze.patch and
the ext4-balloc-fix-_with_rsv-freeze.patch, the resulting comment
goes wrong: there's never been such a freeze in ext3 or ext4.

I suggest a better comment for this ext3 one would be something
like the below - I trust you to deduce the ext4 comment!

Port fix to the off-by-one in find_next_usable_block's memscan from
ext2 to ext3; but it didn't cause a serious problem for ext3 because
the additional ext3_test_allocatable check rescued it from the error.

Hugh

> 
> Fix the range to find_next_usable_block's memscan: the scan from "here"
> (0xcfe) up to (but excluding) "maxblocks" (0xd0e) needs to scan 3 bytes not
> 2 (the relevant bytes of bitmap in this case being f7 df ff - none 00, but
> the premature cutoff implying that the last was found 00).
> 
> Is this a problem for mainline ext3?  No, because the "size" in its memscan
> is always EXT2_BLOCKS_PER_GROUP(sb), which mkfs.ext3 requires to be a
> multiple of 8.  Is this a problem for ext3 or ext4?  No, because they have
> an additional extN_test_allocatable test which rescues them from the error.
> 
> Signed-off-by: Mingming Cao <cmm@...ibm.com>
> Signed-off-by: Hugh Dickins <hugh@...itas.com>
> Cc: <linux-ext4@...r.kernel.org>
> Signed-off-by: Andrew Morton <akpm@...l.org>
> ---
> 
>  fs/ext3/balloc.c |    2 +-
>  1 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff -puN fs/ext3/balloc.c~ext3-balloc-fix-_with_rsv-freeze fs/ext3/balloc.c
> --- a/fs/ext3/balloc.c~ext3-balloc-fix-_with_rsv-freeze
> +++ a/fs/ext3/balloc.c
> @@ -730,7 +730,7 @@ find_next_usable_block(ext3_grpblk_t sta
>  		here = 0;
>  
>  	p = ((char *)bh->b_data) + (here >> 3);
> -	r = memscan(p, 0, (maxblocks - here + 7) >> 3);
> +	r = memscan(p, 0, ((maxblocks + 7) >> 3) - (here >> 3));
>  	next = (r - ((char *)bh->b_data)) << 3;
>  
>  	if (next < maxblocks && next >= start && ext3_test_allocatable(next, bh))
> _
> 
> Patches currently in -mm which might be from hugh@...itas.com are
> 
> git-powerpc.patch
> __unmap_hugepage_range-add-comment.patch
> shared-page-table-for-hugetlb-page-v4.patch
> htlb-forget-rss-with-pt-sharing.patch
> mlock-cleanup.patch
> always-print-out-the-header-line-in-proc-swaps.patch
> reject-corrupt-swapfiles-earlier.patch
> kill-install_file_ptes-pte_val.patch
> honour-mnt_noexec-for-access.patch
> ext3-fix-reservation-extension.patch
> ext4-fix-reservation-extension.patch
> ext3-balloc-reset-windowsz-when-full.patch
> ext3-balloc-fix-off-by-one-against-grp_goal.patch
> ext3-balloc-fix-off-by-one-against-rsv_end.patch
> ext3-balloc-say-rb_entry-not-list_entry.patch
> ext3-balloc-use-io_error-label.patch
> ext3-balloc-fix-_with_rsv-freeze.patch
> ext2-reservations.patch
> ext2-balloc-fix-_with_rsv-freeze.patch
> ext2-balloc-reset-windowsz-when-full.patch
> ext2-balloc-fix-off-by-one-against-rsv_end.patch
> ext2-balloc-fix-off-by-one-against-grp_goal.patch
> ext2-balloc-say-rb_entry-not-list_entry.patch
> ext2-balloc-use-io_error-label.patch
> generic-bug-implementation.patch
> generic-bug-implementation-handle-bug=n.patch
> generic-bug-for-i386.patch
> generic-bug-for-x86-64.patch
> bug-test-1.patch
> tty-switch-to-ktermios-powerpc-fix.patch
-
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