On 8/3/20 4:31 AM, Dave Chinner wrote:
On Wed, Jul 29, 2020 at 02:15:18PM +0530, Ritesh Harjani wrote:For systems which do not have CONFIG_PREEMPT set and if there is a heavy multi-threaded load/store operation happening on pmem + sometimes along with device latencies, softlockup warnings like this could trigger. This was seen on Power where pagesize is 64K. To avoid softlockup, this patch adds a cond_resched() in this path. <...> watchdog: BUG: soft lockup - CPU#31 stuck for 22s! <...> CPU: 31 PID: 15627 <..> 5.3.18-20 <...> NIP memcpy_power7+0x43c/0x7e0 LR memcpy_flushcache+0x28/0xa0 Call Trace: memcpy_power7+0x274/0x7e0 (unreliable) memcpy_flushcache+0x28/0xa0 write_pmem+0xa0/0x100 [nd_pmem] pmem_do_bvec+0x1f0/0x420 [nd_pmem] pmem_make_request+0x14c/0x370 [nd_pmem] generic_make_request+0x164/0x400 submit_bio+0x134/0x2e0 submit_bio_wait+0x70/0xc0 blkdev_issue_zeroout+0xf4/0x2a0 xfs_zero_extent+0x90/0xc0 [xfs] xfs_bmapi_convert_unwritten+0x198/0x230 [xfs] xfs_bmapi_write+0x284/0x630 [xfs] xfs_iomap_write_direct+0x1f0/0x3e0 [xfs] xfs_file_iomap_begin+0x344/0x690 [xfs] dax_iomap_pmd_fault+0x488/0xc10 __xfs_filemap_fault+0x26c/0x2b0 [xfs] __handle_mm_fault+0x794/0x1af0 handle_mm_fault+0x12c/0x220 __do_page_fault+0x290/0xe40 do_page_fault+0x38/0xc0 handle_page_fault+0x10/0x30 Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com> Signed-off-by: Ritesh Harjani <rite...@linux.ibm.com> --- drivers/nvdimm/pmem.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c index 2df6994acf83..fcf7af13897e 100644 --- a/drivers/nvdimm/pmem.c +++ b/drivers/nvdimm/pmem.c @@ -214,6 +214,7 @@ static blk_qc_t pmem_make_request(struct request_queue *q, struct bio *bio) bio->bi_status = rc; break; } + cond_resched();There are already cond_resched() calls between submitted bios in blkdev_issue_zeroout() via both __blkdev_issue_zero_pages() and __blkdev_issue_write_zeroes(), so I'm kinda wondering where the problem is coming from here.
This problem is coming from that bio call- submit_bio()
Just how big is the bio being issued here that it spins for 22s trying to copy it?
It's 256 (due to BIO_MAX_PAGES) * 64KB (pagesize) = 16MB. So this is definitely not an easy trigger as per tester was mainly seen on a VM. Looking at the cond_resched() inside dax_writeback_mapping_range() in xas_for_each_marked() loop, I thought it should be good to have a cond_resched() in the above path as well. Hence an RFC for discussion.
And, really, if the system is that bound on cacheline bouncing that it prevents memcpy() from making progress, I think we probably should be issuing a soft lockup warning like this... > Cheers, Dave.
