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zvol: Remove broken blk-mq optimization

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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 <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #15351
This commit is contained in:
Tony Hutter 2023-10-23 14:45:06 -07:00
parent 86c3ed40e1
commit e860cb0200
2 changed files with 0 additions and 37 deletions
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8
include/os/linux/spl/sys/uio.h
View File

@ -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);

29
module/os/linux/zfs/zfs_uio.c
View File

@ -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;
}