| Message ID | 20210519135440.26773-1-bostroesser@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | b4150b68815e9e4447ce169224ed436b419f0153 |
| Headers | show |
| Series | [v3] scsi: target: tcmu: Fix xarray RCU warning | expand |
On May 19, 2021 / 15:54, Bodo Stroesser wrote: > Commit f5ce815f34bc ("scsi: target: tcmu: Support DATA_BLOCK_SIZE = N * > PAGE_SIZE") introduced xas_next() calls to iterate xarray elements. > These calls triggered the WARNING "suspicious RCU usage" at tcmu device > set up [1]. In the call stack of xas_next(), xas_load() was called. > According to its comment, this function requires "the xa_lock or the RCU > lock". > > To avoid the warning > - guard the small loop calling xas_next() in tcmu_get_empty_block with > RCU lock > - In the large loop in tcmu_copy_data using RCU lock would possibly > disable preemtion for a long time (copy multi MBs). Therefore replace > XA_STATE, xas_set and xas_next with a single xa_load. > > [1] > > [ 1899.867091] ============================= > [ 1899.871199] WARNING: suspicious RCU usage > [ 1899.875310] 5.13.0-rc1+ #41 Not tainted > [ 1899.879222] ----------------------------- > [ 1899.883299] include/linux/xarray.h:1182 suspicious rcu_dereference_check() usage! > [ 1899.890940] other info that might help us debug this: > [ 1899.899082] rcu_scheduler_active = 2, debug_locks = 1 > [ 1899.905719] 3 locks held by kworker/0:1/1368: > [ 1899.910161] #0: ffffa1f8c8b98738 ((wq_completion)target_submission){+.+.}-{0:0}, at: process_one_work+0x1ee/0x580 > [ 1899.920732] #1: ffffbd7040cd7e78 ((work_completion)(&q->sq.work)){+.+.}-{0:0}, at: process_one_work+0x1ee/0x580 > [ 1899.931146] #2: ffffa1f8d1c99768 (&udev->cmdr_lock){+.+.}-{3:3}, at: tcmu_queue_cmd+0xea/0x160 [target_core_user] > [ 1899.941678] stack backtrace: > [ 1899.946093] CPU: 0 PID: 1368 Comm: kworker/0:1 Not tainted 5.13.0-rc1+ #41 > [ 1899.953070] Hardware name: System manufacturer System Product Name/PRIME Z270-A, BIOS 1302 03/15/2018 > [ 1899.962459] Workqueue: target_submission target_queued_submit_work [target_core_mod] > [ 1899.970337] Call Trace: > [ 1899.972839] dump_stack+0x6d/0x89 > [ 1899.976222] xas_descend+0x10e/0x120 > [ 1899.979875] xas_load+0x39/0x50 > [ 1899.983077] tcmu_get_empty_blocks+0x115/0x1c0 [target_core_user] > [ 1899.989318] queue_cmd_ring+0x1da/0x630 [target_core_user] > [ 1899.994897] ? rcu_read_lock_sched_held+0x3f/0x70 > [ 1899.999695] ? trace_kmalloc+0xa6/0xd0 > [ 1900.003501] ? __kmalloc+0x205/0x380 > [ 1900.007167] tcmu_queue_cmd+0x12f/0x160 [target_core_user] > [ 1900.012746] __target_execute_cmd+0x23/0xa0 [target_core_mod] > [ 1900.018589] transport_generic_new_cmd+0x1f3/0x370 [target_core_mod] > [ 1900.025046] transport_handle_cdb_direct+0x34/0x50 [target_core_mod] > [ 1900.031517] target_queued_submit_work+0x43/0xe0 [target_core_mod] > [ 1900.037837] process_one_work+0x268/0x580 > [ 1900.041952] ? process_one_work+0x580/0x580 > [ 1900.046195] worker_thread+0x55/0x3b0 > [ 1900.049921] ? process_one_work+0x580/0x580 > [ 1900.054192] kthread+0x143/0x160 > [ 1900.057499] ? kthread_create_worker_on_cpu+0x40/0x40 > [ 1900.062661] ret_from_fork+0x1f/0x30 > > Fixes: f5ce815f34bc ("scsi: target: tcmu: Support DATA_BLOCK_SIZE = N * PAGE_SIZE") > Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com> > Signed-off-by: Bodo Stroesser <bostroesser@gmail.com> > --- > Changes from v2: > * In the large loop of tcmu_copy_data use xa_load instead of xas_*. Thank you, Bodo. I confirmed that v3 patch avoids the warning, and it passed my test set. Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
On Wed, 19 May 2021 15:54:40 +0200, Bodo Stroesser wrote: > Commit f5ce815f34bc ("scsi: target: tcmu: Support DATA_BLOCK_SIZE = N * > PAGE_SIZE") introduced xas_next() calls to iterate xarray elements. > These calls triggered the WARNING "suspicious RCU usage" at tcmu device > set up [1]. In the call stack of xas_next(), xas_load() was called. > According to its comment, this function requires "the xa_lock or the RCU > lock". > > [...] Applied to 5.13/scsi-fixes, thanks! [1/1] scsi: target: tcmu: Fix xarray RCU warning https://git.kernel.org/mkp/scsi/c/b4150b68815e
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c index 9866d7b49ab8..806f64a6a779 100644 --- a/drivers/target/target_core_user.c +++ b/drivers/target/target_core_user.c @@ -516,8 +516,10 @@ static inline int tcmu_get_empty_block(struct tcmu_dev *udev, dpi = dbi * udev->data_pages_per_blk; /* Count the number of already allocated pages */ xas_set(&xas, dpi); + rcu_read_lock(); for (cnt = 0; xas_next(&xas) && cnt < page_cnt;) cnt++; + rcu_read_unlock(); for (i = cnt; i < page_cnt; i++) { /* try to get new page from the mm */ @@ -699,11 +701,10 @@ static inline void tcmu_copy_data(struct tcmu_dev *udev, struct scatterlist *sg, unsigned int sg_nents, struct iovec **iov, size_t data_len) { - XA_STATE(xas, &udev->data_pages, 0); /* start value of dbi + 1 must not be a valid dbi */ int dbi = -2; size_t page_remaining, cp_len; - int page_cnt, page_inx; + int page_cnt, page_inx, dpi; struct sg_mapping_iter sg_iter; unsigned int sg_flags; struct page *page; @@ -726,9 +727,10 @@ static inline void tcmu_copy_data(struct tcmu_dev *udev, if (page_cnt > udev->data_pages_per_blk) page_cnt = udev->data_pages_per_blk; - xas_set(&xas, dbi * udev->data_pages_per_blk); - for (page_inx = 0; page_inx < page_cnt && data_len; page_inx++) { - page = xas_next(&xas); + dpi = dbi * udev->data_pages_per_blk; + for (page_inx = 0; page_inx < page_cnt && data_len; + page_inx++, dpi++) { + page = xa_load(&udev->data_pages, dpi); if (direction == TCMU_DATA_AREA_TO_SG) flush_dcache_page(page);
Commit f5ce815f34bc ("scsi: target: tcmu: Support DATA_BLOCK_SIZE = N * PAGE_SIZE") introduced xas_next() calls to iterate xarray elements. These calls triggered the WARNING "suspicious RCU usage" at tcmu device set up [1]. In the call stack of xas_next(), xas_load() was called. According to its comment, this function requires "the xa_lock or the RCU lock". To avoid the warning - guard the small loop calling xas_next() in tcmu_get_empty_block with RCU lock - In the large loop in tcmu_copy_data using RCU lock would possibly disable preemtion for a long time (copy multi MBs). Therefore replace XA_STATE, xas_set and xas_next with a single xa_load. [1] [ 1899.867091] ============================= [ 1899.871199] WARNING: suspicious RCU usage [ 1899.875310] 5.13.0-rc1+ #41 Not tainted [ 1899.879222] ----------------------------- [ 1899.883299] include/linux/xarray.h:1182 suspicious rcu_dereference_check() usage! [ 1899.890940] other info that might help us debug this: [ 1899.899082] rcu_scheduler_active = 2, debug_locks = 1 [ 1899.905719] 3 locks held by kworker/0:1/1368: [ 1899.910161] #0: ffffa1f8c8b98738 ((wq_completion)target_submission){+.+.}-{0:0}, at: process_one_work+0x1ee/0x580 [ 1899.920732] #1: ffffbd7040cd7e78 ((work_completion)(&q->sq.work)){+.+.}-{0:0}, at: process_one_work+0x1ee/0x580 [ 1899.931146] #2: ffffa1f8d1c99768 (&udev->cmdr_lock){+.+.}-{3:3}, at: tcmu_queue_cmd+0xea/0x160 [target_core_user] [ 1899.941678] stack backtrace: [ 1899.946093] CPU: 0 PID: 1368 Comm: kworker/0:1 Not tainted 5.13.0-rc1+ #41 [ 1899.953070] Hardware name: System manufacturer System Product Name/PRIME Z270-A, BIOS 1302 03/15/2018 [ 1899.962459] Workqueue: target_submission target_queued_submit_work [target_core_mod] [ 1899.970337] Call Trace: [ 1899.972839] dump_stack+0x6d/0x89 [ 1899.976222] xas_descend+0x10e/0x120 [ 1899.979875] xas_load+0x39/0x50 [ 1899.983077] tcmu_get_empty_blocks+0x115/0x1c0 [target_core_user] [ 1899.989318] queue_cmd_ring+0x1da/0x630 [target_core_user] [ 1899.994897] ? rcu_read_lock_sched_held+0x3f/0x70 [ 1899.999695] ? trace_kmalloc+0xa6/0xd0 [ 1900.003501] ? __kmalloc+0x205/0x380 [ 1900.007167] tcmu_queue_cmd+0x12f/0x160 [target_core_user] [ 1900.012746] __target_execute_cmd+0x23/0xa0 [target_core_mod] [ 1900.018589] transport_generic_new_cmd+0x1f3/0x370 [target_core_mod] [ 1900.025046] transport_handle_cdb_direct+0x34/0x50 [target_core_mod] [ 1900.031517] target_queued_submit_work+0x43/0xe0 [target_core_mod] [ 1900.037837] process_one_work+0x268/0x580 [ 1900.041952] ? process_one_work+0x580/0x580 [ 1900.046195] worker_thread+0x55/0x3b0 [ 1900.049921] ? process_one_work+0x580/0x580 [ 1900.054192] kthread+0x143/0x160 [ 1900.057499] ? kthread_create_worker_on_cpu+0x40/0x40 [ 1900.062661] ret_from_fork+0x1f/0x30 Fixes: f5ce815f34bc ("scsi: target: tcmu: Support DATA_BLOCK_SIZE = N * PAGE_SIZE") Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com> Signed-off-by: Bodo Stroesser <bostroesser@gmail.com> --- Changes from v2: * In the large loop of tcmu_copy_data use xa_load instead of xas_*. Changes from v1: * Used xas_(un)lock() instead of rcu_read_(un)lock() for the large loop --- drivers/target/target_core_user.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)