drm/xe/eustall: Resolve a possible circular locking dependency

drm/xe/eustall: Resolve a possible circular locking dependency

Use a separate lock in the polling function eu_stall_data_buf_poll()
instead of eu_stall->stream_lock. This would prevent a possible
circular locking dependency leading to a deadlock as described below.
This would also require additional locking with the new lock in
the read function.

<4> [787.192986] ======================================================
<4> [787.192988] WARNING: possible circular locking dependency detected
<4> [787.192991] 6.14.0-rc7-xe+ #1 Tainted: G     U
<4> [787.192993] ------------------------------------------------------
<4> [787.192994] xe_eu_stall/20093 is trying to acquire lock:
<4> [787.192996] ffff88819847e2c0 ((work_completion)
(&(&stream->buf_poll_work)->work)), at: __flush_work+0x1f8/0x5e0
<4> [787.193005] but task is already holding lock:
<4> [787.193007] ffff88814ce83ba8 (&gt->eu_stall->stream_lock){3:3},
at: xe_eu_stall_stream_ioctl+0x41/0x6a0 [xe]
<4> [787.193090] which lock already depends on the new lock.
<4> [787.193093] the existing dependency chain (in reverse order) is:
<4> [787.193095]
-> #1 (&gt->eu_stall->stream_lock){+.+.}-{3:3}:
<4> [787.193099]        __mutex_lock+0xb4/0xe40
<4> [787.193104]        mutex_lock_nested+0x1b/0x30
<4> [787.193106]        eu_stall_data_buf_poll_work_fn+0x44/0x1d0 [xe]
<4> [787.193155]        process_one_work+0x21c/0x740
<4> [787.193159]        worker_thread+0x1db/0x3c0
<4> [787.193161]        kthread+0x10d/0x270
<4> [787.193164]        ret_from_fork+0x44/0x70
<4> [787.193168]        ret_from_fork_asm+0x1a/0x30
<4> [787.193172]
-> #0 ((work_completion)(&(&stream->buf_poll_work)->work)){+.+.}-{0:0}:
<4> [787.193176]        __lock_acquire+0x1637/0x2810
<4> [787.193180]        lock_acquire+0xc9/0x300
<4> [787.193183]        __flush_work+0x219/0x5e0
<4> [787.193186]        cancel_delayed_work_sync+0x87/0x90
<4> [787.193189]        xe_eu_stall_disable_locked+0x9a/0x260 [xe]
<4> [787.193237]        xe_eu_stall_stream_ioctl+0x5b/0x6a0 [xe]
<4> [787.193285]        __x64_sys_ioctl+0xa4/0xe0
<4> [787.193289]        x64_sys_call+0x131e/0x2650
<4> [787.193292]        do_syscall_64+0x91/0x180
<4> [787.193295]        entry_SYSCALL_64_after_hwframe+0x76/0x7e
<4> [787.193299]
other info that might help us debug this:
<4> [787.193302]  Possible unsafe locking scenario:
<4> [787.193304]        CPU0                    CPU1
<4> [787.193305]        ----                    ----
<4> [787.193306]   lock(&gt->eu_stall->stream_lock);
<4> [787.193308]                        lock((work_completion)
					(&(&stream->buf_poll_work)->work));
<4> [787.193311]                        lock(&gt->eu_stall->stream_lock);
<4> [787.193313]   lock((work_completion)
			(&(&stream->buf_poll_work)->work));
<4> [787.193315]
 *** DEADLOCK ***

Fixes: 760edec939685 ("drm/xe/eustall: Add support to read() and poll() EU stall data")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4598
Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://lore.kernel.org/r/c896932fca84f79db2df5942911997ed77b2b9b6.1744934656.git.harish.chegondi@intel.com
(cherry picked from commit c2b1f1b8641372bb2e563c49eb25632623a860fc)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>