From: Eric Biggers <ebiggers@xxxxxxxxxx>
Sent: Friday, December 4, 2020 9:42 PM
> To: Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; viro@xxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; pali@xxxxxxxxxx; dsterba@xxxxxxx;
> aaptel@xxxxxxxx; willy@xxxxxxxxxxxxx; rdunlap@xxxxxxxxxxxxx; joe@xxxxxxxxxxx; mark@xxxxxxxxxxxxx; nborisov@xxxxxxxx;
> linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx; anton@xxxxxxxxxx; dan.carpenter@xxxxxxxxxx; hch@xxxxxx
> Subject: Re: [PATCH v14 04/10] fs/ntfs3: Add file operations and implementation
>
> On Fri, Dec 04, 2020 at 06:45:54PM +0300, Konstantin Komarov wrote:
> > +/* external compression lzx/xpress */
> > +static int decompress_lzx_xpress(struct ntfs_sb_info *sbi, const char *cmpr,
> > + size_t cmpr_size, void *unc, size_t unc_size,
> > + u32 frame_size)
> > +{
> > + int err;
> > + void *ctx;
> > +
> > + if (cmpr_size == unc_size) {
> > + /* frame not compressed */
> > + memcpy(unc, cmpr, unc_size);
> > + return 0;
> > + }
> > +
> > + err = 0;
> > + ctx = NULL;
> > + spin_lock(&sbi->compress.lock);
> > + if (frame_size == 0x8000) {
> > + /* LZX: frame compressed */
> > + if (!sbi->compress.lzx) {
> > + /* Lazy initialize lzx decompress context */
> > + spin_unlock(&sbi->compress.lock);
> > + ctx = lzx_allocate_decompressor(0x8000);
> > + if (!ctx)
> > + return -ENOMEM;
> > + if (IS_ERR(ctx)) {
> > + /* should never failed */
> > + err = PTR_ERR(ctx);
> > + goto out;
> > + }
> > +
> > + spin_lock(&sbi->compress.lock);
> > + if (!sbi->compress.lzx) {
> > + sbi->compress.lzx = ctx;
> > + ctx = NULL;
> > + }
> > + }
> > +
> > + if (lzx_decompress(sbi->compress.lzx, cmpr, cmpr_size, unc,
> > + unc_size)) {
> > + err = -EINVAL;
> > + }
> > + } else {
> > + /* XPRESS: frame compressed */
> > + if (!sbi->compress.xpress) {
> > + /* Lazy initialize xpress decompress context */
> > + spin_unlock(&sbi->compress.lock);
> > + ctx = xpress_allocate_decompressor();
> > + if (!ctx)
> > + return -ENOMEM;
> > +
> > + spin_lock(&sbi->compress.lock);
> > + if (!sbi->compress.xpress) {
> > + sbi->compress.xpress = ctx;
> > + ctx = NULL;
> > + }
> > + }
> > +
> > + if (xpress_decompress(sbi->compress.xpress, cmpr, cmpr_size,
> > + unc, unc_size)) {
> > + err = -EINVAL;
> > + }
> > + }
> > + spin_unlock(&sbi->compress.lock);
> > +out:
> > + ntfs_free(ctx);
> > + return err;
> > +}
>
> Decompression is a somewhat heavyweight operation. Not the type of thing that
> should be done while holding a spin lock.
>
> - Eric
Hi Eric! We plan to swap spinlock to mutex in the next version.
Best regards!
