Re: [PATCH V2] dmaengine: Fix client_count is countered one more incorrectly.

[Joel Savitz]

> I would like to send v3.
> Because the comments provided by Jerry are more detail, i would like
> replace the original with his comments.
> 
> Here's draft,
> 
> dmaengine: Fix double increment of client_count in dma_chan_get()
> 
> The first time dma_chan_get() is called for a channel the channel
> client_count is incorrectly incremented twice for public channels,
> first in balance_ref_count(), and again prior to returning. This
> results in an incorrect client count which will lead to the
> channel resources not being freed when they should be. A simple
> test of repeated module load and unload of async_tx on a Dell
> Power Edge R7425 also shows this resulting in a kref underflow
> warning.
> 
> [  124.329662] async_tx: api initialized (async)
> [  129.000627] async_tx: api initialized (async)
> [  130.047839] ------------[ cut here ]------------
> [  130.052472] refcount_t: underflow; use-after-free.
> [  130.057279] WARNING: CPU: 3 PID: 19364 at lib/refcount.c:28
> refcount_warn_saturate+0xba/0x110
> [  130.065811] Modules linked in: async_tx(-) rfkill intel_rapl_msr
> intel_rapl_common amd64_edac edac_mce_amd ipmi_ssif kvm_amd dcdbas kvm
> mgag200 drm_shmem_helper acpi_ipmi irqbypass drm_kms_helper ipmi_si
> syscopyarea sysfillrect rapl pcspkr ipmi_devintf sysimgblt fb_sys_fops
> k10temp i2c_piix4 ipmi_msghandler acpi_power_meter acpi_cpufreq vfat
> fat drm fuse xfs libcrc32c sd_mod t10_pi sg ahci crct10dif_pclmul
> libahci crc32_pclmul crc32c_intel ghash_clmulni_intel igb megaraid_sas
> i40e libata i2c_algo_bit ccp sp5100_tco dca dm_mirror dm_region_hash
> dm_log dm_mod [last unloaded: async_tx]
> [  130.117361] CPU: 3 PID: 19364 Comm: modprobe Kdump: loaded Not
> tainted 5.14.0-185.el9.x86_64 #1
> [  130.126091] Hardware name: Dell Inc. PowerEdge R7425/02MJ3T, BIOS
> 1.18.0 01/17/2022
> [  130.133806] RIP: 0010:refcount_warn_saturate+0xba/0x110
> [  130.139041] Code: 01 01 e8 6d bd 55 00 0f 0b e9 72 9d 8a 00 80 3d
> 26 18 9c 01 00 75 85 48 c7 c7 f8 a3 03 9d c6 05 16 18 9c 01 01 e8 4a
> bd 55 00 <0f> 0b e9 4f 9d 8a 00 80 3d 01 18 9c 01 00 0f 85 5e ff ff ff
> 48 c7
> [  130.157807] RSP: 0018:ffffbf98898afe68 EFLAGS: 00010286
> [  130.163036] RAX: 0000000000000000 RBX: ffff9da06028e598 RCX: 0000000000000000
> [  130.170172] RDX: ffff9daf9de26480 RSI: ffff9daf9de198a0 RDI: ffff9daf9de198a0
> [  130.177316] RBP: ffff9da7cddf3970 R08: 0000000000000000 R09: 00000000ffff7fff
> [  130.184459] R10: ffffbf98898afd00 R11: ffffffff9d9e8c28 R12: ffff9da7cddf1970
> [  130.191596] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [  130.198739] FS:  00007f646435c740(0000) GS:ffff9daf9de00000(0000)
> knlGS:0000000000000000
> [  130.206832] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  130.212586] CR2: 00007f6463b214f0 CR3: 00000008ab98c000 CR4: 00000000003506e0
> [  130.219729] Call Trace:
> [  130.222192]  <TASK>
> [  130.224305]  dma_chan_put+0x10d/0x110
> [  130.227988]  dmaengine_put+0x7a/0xa0
> [  130.231575]  __do_sys_delete_module.constprop.0+0x178/0x280
> [  130.237157]  ? syscall_trace_enter.constprop.0+0x145/0x1d0
> [  130.242652]  do_syscall_64+0x5c/0x90
> [  130.246240]  ? exc_page_fault+0x62/0x150
> [  130.250178]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [  130.255243] RIP: 0033:0x7f6463a3f5ab
> [  130.258830] Code: 73 01 c3 48 8b 0d 75 a8 1b 00 f7 d8 64 89 01 48
> 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00
> 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 45 a8 1b 00 f7 d8 64 89
> 01 48
> [  130.277591] RSP: 002b:00007fff22f972c8 EFLAGS: 00000206 ORIG_RAX:
> 00000000000000b0
> [  130.285164] RAX: ffffffffffffffda RBX: 000055b6786edd40 RCX: 00007f6463a3f5ab
> [  130.292303] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 000055b6786edda8
> [  130.299443] RBP: 000055b6786edd40 R08: 0000000000000000 R09: 0000000000000000
> [  130.306584] R10: 00007f6463b9eac0 R11: 0000000000000206 R12: 000055b6786edda8
> [  130.313731] R13: 0000000000000000 R14: 000055b6786edda8 R15: 00007fff22f995f8
> [  130.320875]  </TASK>
> [  130.323081] ---[ end trace eff7156d56b5cf25 ]---
> 
> cat /sys/class/dma/dma0chan*/in_use would get the wrong result.
> 2
> 2
> 2

Looks good to me.