Patch "nd_btt: Make BTT lanes preemptible" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nd_btt: Make BTT lanes preemptible

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nd_btt-make-btt-lanes-preemptible.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 179b48fd4d3e191dc3430a57a7c5335ab88b0664
Author: Tomas Glozar <tglozar@xxxxxxxxxx>
Date:   Wed Sep 20 07:37:12 2023 +0200

    nd_btt: Make BTT lanes preemptible
    
    [ Upstream commit 36c75ce3bd299878fd9b238e9803d3817ddafbf3 ]
    
    nd_region_acquire_lane uses get_cpu, which disables preemption. This is
    an issue on PREEMPT_RT kernels, since btt_write_pg and also
    nd_region_acquire_lane itself take a spin lock, resulting in BUG:
    sleeping function called from invalid context.
    
    Fix the issue by replacing get_cpu with smp_process_id and
    migrate_disable when needed. This makes BTT operations preemptible, thus
    permitting the use of spin_lock.
    
    BUG example occurring when running ndctl tests on PREEMPT_RT kernel:
    
    BUG: sleeping function called from invalid context at
    kernel/locking/spinlock_rt.c:48
    in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 4903, name:
    libndctl
    preempt_count: 1, expected: 0
    RCU nest depth: 0, expected: 0
    Preemption disabled at:
    [<ffffffffc1313db5>] nd_region_acquire_lane+0x15/0x90 [libnvdimm]
    Call Trace:
     <TASK>
     dump_stack_lvl+0x8e/0xb0
     __might_resched+0x19b/0x250
     rt_spin_lock+0x4c/0x100
     ? btt_write_pg+0x2d7/0x500 [nd_btt]
     btt_write_pg+0x2d7/0x500 [nd_btt]
     ? local_clock_noinstr+0x9/0xc0
     btt_submit_bio+0x16d/0x270 [nd_btt]
     __submit_bio+0x48/0x80
     __submit_bio_noacct+0x7e/0x1e0
     submit_bio_wait+0x58/0xb0
     __blkdev_direct_IO_simple+0x107/0x240
     ? inode_set_ctime_current+0x51/0x110
     ? __pfx_submit_bio_wait_endio+0x10/0x10
     blkdev_write_iter+0x1d8/0x290
     vfs_write+0x237/0x330
     ...
     </TASK>
    
    Fixes: 5212e11fde4d ("nd_btt: atomic sector updates")
    Signed-off-by: Tomas Glozar <tglozar@xxxxxxxxxx>
    Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
    Reviewed-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
    Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index aac6708d33caa..c79e4219f14dd 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -907,7 +907,8 @@ unsigned int nd_region_acquire_lane(struct nd_region *nd_region)
 {
 	unsigned int cpu, lane;
 
-	cpu = get_cpu();
+	migrate_disable();
+	cpu = smp_processor_id();
 	if (nd_region->num_lanes < nr_cpu_ids) {
 		struct nd_percpu_lane *ndl_lock, *ndl_count;
 
@@ -926,16 +927,15 @@ EXPORT_SYMBOL(nd_region_acquire_lane);
 void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane)
 {
 	if (nd_region->num_lanes < nr_cpu_ids) {
-		unsigned int cpu = get_cpu();
+		unsigned int cpu = smp_processor_id();
 		struct nd_percpu_lane *ndl_lock, *ndl_count;
 
 		ndl_count = per_cpu_ptr(nd_region->lane, cpu);
 		ndl_lock = per_cpu_ptr(nd_region->lane, lane);
 		if (--ndl_count->count == 0)
 			spin_unlock(&ndl_lock->lock);
-		put_cpu();
 	}
-	put_cpu();
+	migrate_enable();
 }
 EXPORT_SYMBOL(nd_region_release_lane);