Hi Joe,
On Tue, Apr 06, 2021 at 08:38:44PM -0700, Joe Perches wrote:
> On Wed, 2021-04-07 at 07:54 +0800, Gao Xiang wrote:
> > Hi Colin,
> >
> > On Tue, Apr 06, 2021 at 05:27:18PM +0100, Colin King wrote:
> > > From: Colin Ian King <colin.k...@canonical.com>
> > >
> > > The while-loop iterates until src is non-null or i is 3, however, the
> > > loop counter i is not intinitialied to zero, causing incorrect iteration
> > > counts. Fix this by initializing it to zero.
> > >
> > > Addresses-Coverity: ("Uninitialized scalar variable")
> > > Fixes: 1aa5f2e2feed ("erofs: support decompress big pcluster for lz4
> > > backend")
> > > Signed-off-by: Colin Ian King <colin.k...@canonical.com>
> >
> > Thank you very much for catching this! It looks good to me,
> > Reviewed-by: Gao Xiang <hsiang...@redhat.com>
> >
> > (btw, may I fold this into the original patchset? since such big pcluster
> > patchset is just applied to for-next for further integration testing, and
> > the commit id is not stable yet..)
> >
> > Thanks,
> > Gao Xiang
>
> I think this code is odd and would be more intelligible using
> a for loop like:
Thanks for your reply/suggestion.
> ---
> fs/erofs/decompressor.c | 20 ++++++++------------
> 1 file changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 27aa6a99b371..5a64f4649414 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -286,28 +286,24 @@ static int z_erofs_decompress_generic(struct
> z_erofs_decompress_req *rq,
> }
>
> ret = alg->prepare_destpages(rq, pagepool);
> - if (ret < 0) {
> + if (ret < 0)
> return ret;
> - } else if (ret) {
> + if (ret) {
> dst = page_address(*rq->out);
> dst_maptype = 1;
> goto dstmap_out;
> }
I agree with the modification here, thanks!
>
> - i = 0;
> - while (1) {
> + for (i = 0; i < 3; i++) {
> dst = vm_map_ram(rq->out, nrpages_out, -1);
> -
> + if (dst) {
> + dst_maptype = 2;
> + goto dstmap_out;
> + }
> /* retry two more times (totally 3 times) */
> - if (dst || ++i >= 3)
> - break;
> vm_unmap_aliases();
That is not quite equivalent, since after trying more than 3 times,
(I think) no need to do the final vm_unmap_aliases(), since it's
only used for the next vm_map_ram(). Similar logic also see:
fs/xfs/xfs_buf.c: _xfs_buf_map_pages():
/*
* vm_map_ram() will allocate auxiliary structures (e.g.
* pagetables) with GFP_KERNEL, yet we are likely to be under
* GFP_NOFS context here. Hence we need to tell memory reclaim
* that we are in such a context via PF_MEMALLOC_NOFS to prevent
* memory reclaim re-entering the filesystem here and
* potentially deadlocking.
*/
nofs_flag = memalloc_nofs_save();
do {
bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
-1);
if (bp->b_addr)
break;
vm_unmap_aliases();
} while (retried++ <= 1);
memalloc_nofs_restore(nofs_flag);
if (!bp->b_addr)
return -ENOMEM;
but yeah with some modification (and extra vm_unmap_aliases() here
as well...)
Thanks,
Gao Xiang
