s390/debug: Convert debug area lock from a spinlock to a raw spinlock

s390/debug: Convert debug area lock from a spinlock to a raw spinlock

With PREEMPT_RT as potential configuration option, spinlock_t is now
considered as a sleeping lock, and thus might cause issues when used in
an atomic context. But even with PREEMPT_RT as potential configuration
option, raw_spinlock_t remains as a true spinning lock/atomic context.
This creates potential issues with the s390 debug/tracing feature. The
functions to trace errors are called in various contexts, including
under lock of raw_spinlock_t, and thus the used spinlock_t in each debug
area is in violation of the locking semantics.

Here are two examples involving failing PCI Read accesses that are
traced while holding `pci_lock` in `drivers/pci/access.c`:

=============================
[ BUG: Invalid wait context ]
6.19.0-devel #18 Not tainted
-----------------------------
bash/3833 is trying to lock:
0000027790baee30 (&rc->lock){-.-.}-{3:3}, at: debug_event_common+0xfc/0x300
other info that might help us debug this:
context-{5:5}
5 locks held by bash/3833:
 #0: 0000027efbb29450 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x7c/0xf0
 #1: 00000277f0504a90 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x13e/0x260
 #2: 00000277beed8c18 (kn->active#339){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x164/0x260
 #3: 00000277e9859190 (&dev->mutex){....}-{4:4}, at: pci_dev_lock+0x2e/0x40
 #4: 00000383068a7708 (pci_lock){....}-{2:2}, at: pci_bus_read_config_dword+0x4a/0xb0
stack backtrace:
CPU: 6 UID: 0 PID: 3833 Comm: bash Kdump: loaded Not tainted 6.19.0-devel #18 PREEMPTLAZY
Hardware name: IBM 9175 ME1 701 (LPAR)
Call Trace:
 [<00000383048afec2>] dump_stack_lvl+0xa2/0xe8
 [<00000383049ba166>] __lock_acquire+0x816/0x1660
 [<00000383049bb1fa>] lock_acquire+0x24a/0x370
 [<00000383059e3860>] _raw_spin_lock_irqsave+0x70/0xc0
 [<00000383048bbb6c>] debug_event_common+0xfc/0x300
 [<0000038304900b0a>] __zpci_load+0x17a/0x1f0
 [<00000383048fad88>] pci_read+0x88/0xd0
 [<00000383054cbce0>] pci_bus_read_config_dword+0x70/0xb0
 [<00000383054d55e4>] pci_dev_wait+0x174/0x290
 [<00000383054d5a3e>] __pci_reset_function_locked+0xfe/0x170
 [<00000383054d9b30>] pci_reset_function+0xd0/0x100
 [<00000383054ee21a>] reset_store+0x5a/0x80
 [<0000038304e98758>] kernfs_fop_write_iter+0x1e8/0x260
 [<0000038304d995da>] new_sync_write+0x13a/0x180
 [<0000038304d9c5d0>] vfs_write+0x200/0x330
 [<0000038304d9c88c>] ksys_write+0x7c/0xf0
 [<00000383059cfa80>] __do_syscall+0x210/0x500
 [<00000383059e4c06>] system_call+0x6e/0x90
INFO: lockdep is turned off.

=============================
[ BUG: Invalid wait context ]
6.19.0-devel #3 Not tainted
-----------------------------
bash/6861 is trying to lock:
0000009da05c7430 (&rc->lock){-.-.}-{3:3}, at: debug_event_common+0xfc/0x300
other info that might help us debug this:
context-{5:5}
5 locks held by bash/6861:
 #0: 000000acff404450 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x7c/0xf0
 #1: 000000acff41c490 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x13e/0x260
 #2: 0000009da36937d8 (kn->active#75){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x164/0x260
 #3: 0000009dd15250d0 (&zdev->state_lock){+.+.}-{4:4}, at: enable_slot+0x2e/0xc0
 #4: 000001a19682f708 (pci_lock){....}-{2:2}, at: pci_bus_read_config_byte+0x42/0xa0
stack backtrace:
CPU: 16 UID: 0 PID: 6861 Comm: bash Kdump: loaded Not tainted 6.19.0-devel #3 PREEMPTLAZY
Hardware name: IBM 9175 ME1 701 (LPAR)
Call Trace:
 [<000001a194837ec2>] dump_stack_lvl+0xa2/0xe8
 [<000001a194942166>] __lock_acquire+0x816/0x1660
 [<000001a1949431fa>] lock_acquire+0x24a/0x370
 [<000001a19596b810>] _raw_spin_lock_irqsave+0x70/0xc0
 [<000001a194843b6c>] debug_event_common+0xfc/0x300
 [<000001a194888b0a>] __zpci_load+0x17a/0x1f0
 [<000001a194882d88>] pci_read+0x88/0xd0
 [<000001a195453b88>] pci_bus_read_config_byte+0x68/0xa0
 [<000001a195457bc2>] pci_setup_device+0x62/0xad0
 [<000001a195458e70>] pci_scan_single_device+0x90/0xe0
 [<000001a19488a0f6>] zpci_bus_scan_device+0x46/0x80
 [<000001a19547f958>] enable_slot+0x98/0xc0
 [<000001a19547f134>] power_write_file+0xc4/0x110
 [<000001a194e20758>] kernfs_fop_write_iter+0x1e8/0x260
 [<000001a194d215da>] new_sync_write+0x13a/0x180
 [<000001a194d245d0>] vfs_write+0x200/0x330
 [<000001a194d2488c>] ksys_write+0x7c/0xf0
 [<000001a195957a30>] __do_syscall+0x210/0x500
 [<000001a19596cbb6>] system_call+0x6e/0x90
INFO: lockdep is turned off.

Since it is desired to keep it possible to create trace records in most
situations, including this particular case (failing PCI config space
accesses are relevant), convert the used spinlock_t in `struct
debug_info` to raw_spinlock_t.

The impact is small, as the debug area lock only protects bounded memory
access without external dependencies, apart from one function
debug_set_size() where kfree() is implicitly called with the lock held.
Move debug_info_free() out of this lock, to keep remove this external
dependency.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>