On Tue, Jun 02, 2015 at 02:24:50PM +0200, Lukas Czerner wrote:
> Currently ext4_mb_good_group() only returns 0 or 1 depending on whether
> the allocation group is suitable for use or not. However we might get
> various errors and fail while initializing new group including -EIO
> which would never get propagated up the call chain. This might lead to
> an endless loop at writeback when we're trying to find a good group to
> allocate from and we fail to initialize new group (read error for
> example).
>
> Fix this by returning proper error code from ext4_mb_good_group() and
> using it in ext4_mb_regular_allocator(). In ext4_mb_regular_allocator()
> we will always return only the first occurred error from
> ext4_mb_good_group() and we only propagate it back to the caller if we
> do not get any other errors and we fail to allocate any blocks.
>
> Note that with other modes than errors=continue, we will fail
> immediately in ext4_mb_good_group() in case of error, however with
> errors=continue we should try to continue using the file system, that's
> why we're not going to fail immediately when we see an error from
> ext4_mb_good_group(), but rather when we fail to find a suitable block
> group to allocate from due to an problem in group initialization.
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> ---
> v2: nothing changed
>
> fs/ext4/mballoc.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index df02951..e0e77a7 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2034,7 +2034,7 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
I'd prefer a comment clarifying the possible return values. Otherwise,
everything (patches 1-3) looks ok to me.
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
> int ret = ext4_mb_init_group(ac->ac_sb, group);
> if (ret)
> - return 0;
> + return ret;
> }
>
> fragments = grp->bb_fragments;
> @@ -2081,7 +2081,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> {
> ext4_group_t ngroups, group, i;
> int cr;
> - int err = 0;
> + int err = 0, first_err = 0;
> struct ext4_sb_info *sbi;
> struct super_block *sb;
> struct ext4_buddy e4b;
> @@ -2148,6 +2148,7 @@ repeat:
> group = ac->ac_g_ex.fe_group;
>
> for (i = 0; i < ngroups; group++, i++) {
> + int ret = 0;
> cond_resched();
> /*
> * Artificially restricted ngroups for non-extent
> @@ -2157,8 +2158,12 @@ repeat:
> group = 0;
>
> /* This now checks without needing the buddy page */
> - if (!ext4_mb_good_group(ac, group, cr))
> + ret = ext4_mb_good_group(ac, group, cr);
> + if (ret <= 0) {
> + if (!first_err)
> + first_err = ret;
> continue;
> + }
>
> err = ext4_mb_load_buddy(sb, group, &e4b);
> if (err)
> @@ -2170,9 +2175,12 @@ repeat:
> * We need to check again after locking the
> * block group
> */
> - if (!ext4_mb_good_group(ac, group, cr)) {
> + ret = ext4_mb_good_group(ac, group, cr);
> + if (ret <= 0) {
> ext4_unlock_group(sb, group);
> ext4_mb_unload_buddy(&e4b);
> + if (!first_err)
> + first_err = ret;
> continue;
> }
>
> @@ -2219,6 +2227,8 @@ repeat:
> }
> }
> out:
> + if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
> + err = first_err;
> return err;
> }
>
> --
> 1.8.3.1
>
> --
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