From 7c9b6fed16ed5034fd1cdfdaedfad93dc97b1557 Mon Sep 17 00:00:00 2001 From: Tony Hutter Date: Mon, 23 Oct 2023 14:45:06 -0700 Subject: [PATCH] zvol: Remove broken blk-mq optimization This fix removes a dubious optimization in zfs_uiomove_bvec_rq() that saved the iterator contents of a rq_for_each_segment(). This optimization allowed restoring the "saved state" from a previous rq_for_each_segment() call on the same uio so that you wouldn't need to iterate though each bvec on every zfs_uiomove_bvec_rq() call. However, if the kernel is manipulating the requests/bios/bvecs under the covers between zfs_uiomove_bvec_rq() calls, then it could result in corruption from using the "saved state". This optimization results in an unbootable system after installing an OS on a zvol with blk-mq enabled. Reviewed-by: Brian Behlendorf Signed-off-by: Tony Hutter Closes #15351 --- include/os/linux/spl/sys/uio.h | 8 -------- module/os/linux/zfs/zfs_uio.c | 29 ----------------------------- 2 files changed, 37 deletions(-) diff --git a/include/os/linux/spl/sys/uio.h b/include/os/linux/spl/sys/uio.h index cce097e16f..a4b600004c 100644 --- a/include/os/linux/spl/sys/uio.h +++ b/include/os/linux/spl/sys/uio.h @@ -73,13 +73,6 @@ typedef struct zfs_uio { size_t uio_skip; struct request *rq; - - /* - * Used for saving rq_for_each_segment() state between calls - * to zfs_uiomove_bvec_rq(). - */ - struct req_iterator iter; - struct bio_vec bv; } zfs_uio_t; @@ -138,7 +131,6 @@ zfs_uio_bvec_init(zfs_uio_t *uio, struct bio *bio, struct request *rq) } else { uio->uio_bvec = NULL; uio->uio_iovcnt = 0; - memset(&uio->iter, 0, sizeof (uio->iter)); } uio->uio_loffset = io_offset(bio, rq); diff --git a/module/os/linux/zfs/zfs_uio.c b/module/os/linux/zfs/zfs_uio.c index 3efd4ab159..c2ed67c438 100644 --- a/module/os/linux/zfs/zfs_uio.c +++ b/module/os/linux/zfs/zfs_uio.c @@ -204,22 +204,6 @@ zfs_uiomove_bvec_rq(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio) this_seg_start = orig_loffset; rq_for_each_segment(bv, rq, iter) { - if (uio->iter.bio) { - /* - * If uio->iter.bio is present, then we know we've saved - * uio->iter from a previous call to this function, and - * we can skip ahead in this rq_for_each_segment() loop - * to where we last left off. That way, we don't need - * to iterate over tons of segments we've already - * processed - we can just restore the "saved state". - */ - iter = uio->iter; - bv = uio->bv; - this_seg_start = uio->uio_loffset; - memset(&uio->iter, 0, sizeof (uio->iter)); - continue; - } - /* * Lookup what the logical offset of the last byte of this * segment is. @@ -260,19 +244,6 @@ zfs_uiomove_bvec_rq(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio) copied = 1; /* We copied some data */ } - if (n == 0) { - /* - * All done copying. Save our 'iter' value to the uio. - * This allows us to "save our state" and skip ahead in - * the rq_for_each_segment() loop the next time we call - * call zfs_uiomove_bvec_rq() on this uio (which we - * will be doing for any remaining data in the uio). - */ - uio->iter = iter; /* make a copy of the struct data */ - uio->bv = bv; - return (0); - } - this_seg_start = this_seg_end + 1; }