[PATCH v2] sbitmap: Silence a debug kernel warning triggered by sbitmap_put()

All sbitmap code uses implied preemption protection to update
sb->alloc_hint except sbitmap_put(). Using implied preemption protection
is safe since the value of sb->alloc_hint only affects performance of
sbitmap allocations but not their correctness. Change this_cpu_ptr() in
sbitmap_put() into raw_cpu_ptr() to suppress the following kernel warning
that appears with preemption debugging enabled (CONFIG_DEBUG_PREEMPT):

BUG: using smp_processor_id() in preemptible [00000000] code: scsi_eh_0/152
caller is debug_smp_processor_id+0x17/0x20
CPU: 1 PID: 152 Comm: scsi_eh_0 Tainted: G        W         5.12.0-rc1-dbg+ #6
Call Trace:
 show_stack+0x52/0x58
 dump_stack+0xaf/0xf3
 check_preemption_disabled+0xce/0xd0
 debug_smp_processor_id+0x17/0x20
 scsi_device_unbusy+0x13a/0x1c0 [scsi_mod]
 scsi_finish_command+0x4d/0x290 [scsi_mod]
 scsi_eh_flush_done_q+0x1e7/0x280 [scsi_mod]
 ata_scsi_port_error_handler+0x592/0x750 [libata]
 ata_scsi_error+0x1a0/0x1f0 [libata]
 scsi_error_handler+0x19e/0x330 [scsi_mod]
 kthread+0x222/0x250
 ret_from_fork+0x1f/0x30

Reviewed-by: Ming Lei <redacted>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Omar Sandoval <redacted>
Fixes: c548e62bcf6a ("scsi: sbitmap: Move allocation hint into sbitmap")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---

Changes compared to v1: changed patch subject and elaborated patch
description.

 include/linux/sbitmap.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 3087e1f15fdd..2713e689ad66 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h

@@ -324,7 +324,7 @@ static inline void sbitmap_put(struct sbitmap *sb, unsigned int bitnr)
 	sbitmap_deferred_clear_bit(sb, bitnr);
 
 	if (likely(sb->alloc_hint && !sb->round_robin && bitnr < sb->depth))
-		*this_cpu_ptr(sb->alloc_hint) = bitnr;
+		*raw_cpu_ptr(sb->alloc_hint) = bitnr;
 }
 
 static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

On Tue, 16 Mar 2021 20:26:48 -0700, Bart Van Assche wrote:

All sbitmap code uses implied preemption protection to update
sb->alloc_hint except sbitmap_put(). Using implied preemption protection
is safe since the value of sb->alloc_hint only affects performance of
sbitmap allocations but not their correctness. Change this_cpu_ptr() in
sbitmap_put() into raw_cpu_ptr() to suppress the following kernel warning
that appears with preemption debugging enabled (CONFIG_DEBUG_PREEMPT):

[...]

Applied to 5.13/scsi-queue, thanks!

[1/1] sbitmap: Silence a debug kernel warning triggered by sbitmap_put()
      https://git.kernel.org/mkp/scsi/c/035e9f471691

-- 
Martin K. Petersen	Oracle Linux Engineering