[powerpc] WARN at drivers/scsi/sg.c:2236 (sg_remove_sfp_usercontext)

[Sachin Sant]

Following WARN_ON_ONCE is triggered while running LTP tests
(specifically ioctl_sg01) on IBM Power booted with 6.9.0-rc1-next-20240328

[   64.230233] ------------[ cut here ]------------
[   64.230269] WARNING: CPU: 10 PID: 452 at drivers/scsi/sg.c:2236 sg_remove_sfp_usercontext+0x270/0x280 [sg]
[   64.230302] Modules linked in: rpadlpar_io rpaphp xsk_diag nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 bonding tls rfkill ip_set nf_tables nfnetlink sunrpc binfmt_misc pseries_rng vmx_crypto xfs libcrc32c sd_mod sr_mod t10_pi crc64_rocksoft_generic cdrom crc64_rocksoft crc64 sg ibmvscsi ibmveth scsi_transport_srp fuse
[   64.230420] CPU: 10 PID: 452 Comm: kworker/10:1 Kdump: loaded Not tainted 6.9.0-rc1-next-20240328 #2
[   64.230438] Hardware name: IBM,9080-HEX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1060.00 (NH1060_018) hv:phyp pSeries
[   64.230449] Workqueue: events sg_remove_sfp_usercontext [sg]
[   64.230468] NIP:  c008000015c34110 LR: c008000015c33ffc CTR: c0000000005393b0
[   64.230485] REGS: c00000000c1efae0 TRAP: 0700   Not tainted  (6.9.0-rc1-next-20240328)
[   64.230498] MSR:  800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 44000408  XER: 00000000
[   64.230535] CFAR: c008000015c3400c IRQMASK: 0
[   64.230535] GPR00: c008000015c33ffc c00000000c1efd80 c008000015c58900 c00000000ca8ae98
[   64.230535] GPR04: 00000000c0000000 0000000000000023 c000000007c2e000 0000000000000022
[   64.230535] GPR08: 000000038a130000 0000000000000002 0000000000000000 c008000015c38bc0
[   64.230535] GPR12: c0000000005393b0 c00000038fff3f00 c0000000001a2bac c000000007c7a9c0
[   64.230535] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   64.230535] GPR20: c00000038c3f3b00 c000000007c10030 c000000007c10000 c0000000901c0000
[   64.230535] GPR24: 0000000000000000 c00000000ca8ae00 c0000000045a5805 c000000007c11330
[   64.230535] GPR28: c00000038c3f3b00 c000000007c10080 c000000007c11328 c000000002fdee54
[   64.230671] NIP [c008000015c34110] sg_remove_sfp_usercontext+0x270/0x280 [sg]
[   64.230690] LR [c008000015c33ffc] sg_remove_sfp_usercontext+0x15c/0x280 [sg]
[   64.230709] Call Trace:
[   64.230716] [c00000000c1efd80] [c008000015c33ffc] sg_remove_sfp_usercontext+0x15c/0x280 [sg] (unreliable)
[   64.230740] [c00000000c1efe40] [c00000000019337c] process_one_work+0x20c/0x4f4
[   64.230767] [c00000000c1efef0] [c0000000001942fc] worker_thread+0x378/0x544
[   64.230787] [c00000000c1eff90] [c0000000001a2cdc] kthread+0x138/0x140
[   64.230801] [c00000000c1effe0] [c00000000000df98] start_kernel_thread+0x14/0x18
[   64.230819] Code: e8c98310 3d220000 e8698010 480044bd e8410018 7ec3b378 48004ac9 e8410018 38790098 81390098 2c090001 4182ff04 <0fe00000> 4bfffefc 000247e0 00000000
[   64.230857] ---[ end trace 0000000000000000 ]—

This WARN_ON was introduced with
commit 27f58c04a8f438078583041468ec60597841284d
    scsi: sg: Avoid sg device teardown race

Reverting the patch avoids the warning. The test case passes irrespective of the
patch is present of not. 

-- Sachin