linux-ext4 - [RFC 1/1] pmem: Add cond_resched() in bio_for_each_segment loop in pmem_make

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Message-Id: <0d96e2481f292de2cda8828b03d5121004308759.1596011292.git.riteshh@linux.ibm.com>
Date:   Wed, 29 Jul 2020 14:15:18 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-nvdimm@...ts.01.org
Cc:     linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>
Subject: [RFC 1/1] pmem: Add cond_resched() in bio_for_each_segment loop in pmem_make_request

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.kumar@...ux.ibm.com>
Signed-off-by: Ritesh Harjani <riteshh@...ux.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();
 	}
 	if (do_acct)
 		nd_iostat_end(bio, start);
-- 
2.25.4