From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: zram: handle multiple pages attached bio's bvec
Patch series "zram clean up", v2.
This patchset aims to clean up zram .
[1] clean up multiple pages's bvec handling.
[2] clean up partial IO handling
[3-6] clean up zram via using accessor and removing pointless structure.
With [2-6] applied, we can get a few hundred bytes as well as huge
readibility enhance.
x86: 708 byte save
add/remove: 1/1 grow/shrink: 0/11 up/down: 478/-1186 (-708)
function old new delta
zram_special_page_read - 478 +478
zram_reset_device 317 314 -3
mem_used_max_store 131 128 -3
compact_store 96 93 -3
mm_stat_show 203 197 -6
zram_add 719 712 -7
zram_slot_free_notify 229 214 -15
zram_make_request 819 803 -16
zram_meta_free 128 111 -17
zram_free_page 180 151 -29
disksize_store 432 361 -71
zram_decompress_page.isra 504 - -504
zram_bvec_rw 2592 2080 -512
Total: Before=25350773, After=25350065, chg -0.00%
ppc64: 231 byte save
add/remove: 2/0 grow/shrink: 1/9 up/down: 681/-912 (-231)
function old new delta
zram_special_page_read - 480 +480
zram_slot_lock - 200 +200
vermagic 39 40 +1
mm_stat_show 256 248 -8
zram_meta_free 200 184 -16
zram_add 944 912 -32
zram_free_page 348 308 -40
disksize_store 572 492 -80
zram_decompress_page 664 564 -100
zram_slot_free_notify 292 160 -132
zram_make_request 1132 1000 -132
zram_bvec_rw 2768 2396 -372
Total: Before=17565825, After=17565594, chg -0.00%
This patch (of 6):
Johannes Thumshirn reported system goes the panic when using NVMe over
Fabrics loopback target with zram.
The reason is zram expects each bvec in bio contains a single page
but nvme can attach a huge bulk of pages attached to the bio's bvec
so that zram's index arithmetic could be wrong so that out-of-bound
access makes system panic.
[1] in mainline solved solved the problem by limiting max_sectors with
SECTORS_PER_PAGE but it makes zram slow because bio should split with
each pages so this patch makes zram aware of multiple pages in a bvec
so it could solve without any regression(ie, bio split).
[1] 0bc315381fe9, zram: set physical queue limits to avoid array out of
bounds accesses
Link: http://lkml.kernel.org/r/20170413134057.GA27499@bbox
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Reported-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Tested-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 40 ++++++++------------------------
1 file changed, 11 insertions(+), 29 deletions(-)
diff -puN drivers/block/zram/zram_drv.c~zram-handle-multiple-pages-attached-bios-bvec drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c~zram-handle-multiple-pages-attached-bios-bvec
+++ a/drivers/block/zram/zram_drv.c
@@ -137,8 +137,7 @@ static inline bool valid_io_request(stru
static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
{
- if (*offset + bvec->bv_len >= PAGE_SIZE)
- (*index)++;
+ *index += (*offset + bvec->bv_len) / PAGE_SIZE;
*offset = (*offset + bvec->bv_len) % PAGE_SIZE;
}
@@ -840,34 +839,21 @@ static void __zram_make_request(struct z
}
bio_for_each_segment(bvec, bio, iter) {
- int max_transfer_size = PAGE_SIZE - offset;
-
- if (bvec.bv_len > max_transfer_size) {
- /*
- * zram_bvec_rw() can only make operation on a single
- * zram page. Split the bio vector.
- */
- struct bio_vec bv;
-
- bv.bv_page = bvec.bv_page;
- bv.bv_len = max_transfer_size;
- bv.bv_offset = bvec.bv_offset;
+ struct bio_vec bv = bvec;
+ unsigned int unwritten = bvec.bv_len;
+ do {
+ bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
+ unwritten);
if (zram_bvec_rw(zram, &bv, index, offset,
- op_is_write(bio_op(bio))) < 0)
+ op_is_write(bio_op(bio))) < 0)
goto out;
- bv.bv_len = bvec.bv_len - max_transfer_size;
- bv.bv_offset += max_transfer_size;
- if (zram_bvec_rw(zram, &bv, index + 1, 0,
- op_is_write(bio_op(bio))) < 0)
- goto out;
- } else
- if (zram_bvec_rw(zram, &bvec, index, offset,
- op_is_write(bio_op(bio))) < 0)
- goto out;
+ bv.bv_offset += bv.bv_len;
+ unwritten -= bv.bv_len;
- update_position(&index, &offset, &bvec);
+ update_position(&index, &offset, &bv);
+ } while (unwritten);
}
bio_endio(bio);
@@ -884,8 +870,6 @@ static blk_qc_t zram_make_request(struct
{
struct zram *zram = queue->queuedata;
- blk_queue_split(queue, &bio, queue->bio_split);
-
if (!valid_io_request(zram, bio->bi_iter.bi_sector,
bio->bi_iter.bi_size)) {
atomic64_inc(&zram->stats.invalid_io);
@@ -1193,8 +1177,6 @@ static int zram_add(void)
blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
- zram->disk->queue->limits.max_sectors = SECTORS_PER_PAGE;
- zram->disk->queue->limits.chunk_sectors = 0;
blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);
_
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