pmem_submit_bio() passes the parent bio to nvdimm_flush() for REQ_FUA. For virtio-pmem this makes async_pmem_flush() allocate and submit a child PREFLUSH bio chained to the parent.
That child allocation is in the block submit path. Making it blocking with GFP_NOIO can consume the same global bio mempool that submit_bio() uses, while making it GFP_ATOMIC can fail under pressure. A forced failure of the child allocation produced: virtio_pmem: forcing child bio allocation failure for test Buffer I/O error on dev pmem0, logical block 0, lost sync page write EXT4-fs (pmem0): I/O error while writing superblock EXT4-fs (pmem0): mount failed Avoid the child bio completely. Flush FUA synchronously, like REQ_PREFLUSH, then complete the parent after the flush. Since no child bio can be created, async_pmem_flush() now only issues the virtio flush and preserves negative errno values. Signed-off-by: Li Chen <[email protected]> --- Changes in v6: - Replace the child bio allocation fix with synchronous FUA flushing. drivers/nvdimm/nd_virtio.c | 22 ++++------------------ drivers/nvdimm/pmem.c | 2 +- 2 files changed, 5 insertions(+), 19 deletions(-) diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c index 4176046627beb..4b2e9c47af0f5 100644 --- a/drivers/nvdimm/nd_virtio.c +++ b/drivers/nvdimm/nd_virtio.c @@ -110,27 +110,13 @@ static int virtio_pmem_flush(struct nd_region *nd_region) /* The asynchronous flush callback function */ int async_pmem_flush(struct nd_region *nd_region, struct bio *bio) { - /* - * Create child bio for asynchronous flush and chain with - * parent bio. Otherwise directly call nd_region flush. - */ - if (bio && bio->bi_iter.bi_sector != -1) { - struct bio *child = bio_alloc(bio->bi_bdev, 0, - REQ_OP_WRITE | REQ_PREFLUSH, - GFP_ATOMIC); + int err; - if (!child) - return -ENOMEM; - bio_clone_blkg_association(child, bio); - child->bi_iter.bi_sector = -1; - bio_chain(child, bio); - submit_bio(child); - return 0; - } - if (virtio_pmem_flush(nd_region)) + err = virtio_pmem_flush(nd_region); + if (err > 0) return -EIO; - return 0; + return err; }; EXPORT_SYMBOL_GPL(async_pmem_flush); MODULE_DESCRIPTION("Virtio Persistent Memory Driver"); diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c index 82ee1ddb3a445..058d2739c95a1 100644 --- a/drivers/nvdimm/pmem.c +++ b/drivers/nvdimm/pmem.c @@ -242,7 +242,7 @@ static void pmem_submit_bio(struct bio *bio) } if ((bio->bi_opf & REQ_FUA) && !bio->bi_status) - ret = nvdimm_flush(nd_region, bio); + ret = nvdimm_flush(nd_region, NULL); if (ret) bio->bi_status = errno_to_blk_status(ret); -- 2.52.0
