[Bug 94631] New: [dmabuf] import/export/removal is too slow

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94631

            Bug ID: 94631
           Summary: [dmabuf] import/export/removal is too slow
           Product: DRI
           Version: DRI git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: chris at chris-wilson.co.uk
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

drm_prime walks a *list* of dmabuf on

drm_gem_prime_handle_to_fd()
drm_gem_prime_fd_to_handle()

and upon object close, for a kind-off pointless uABI but meh.

/* initial implementaton using a linked list - todo hashtab */
struct drm_prime_file_private {
        struct list_head head;
        struct mutex lock;
};


Running 4KiB-thrash-dmabuf-* is enough to trigger lockups

[94466.160428] INFO: rcu_sched self-detected stall on CPU
[94466.160460]     1-...: (5250 ticks this GP) idle=ed9/140000000000001/0
softirq=17706827/17706827 fqs=5222 
[94466.160473]      (t=5250 jiffies g=2984079 c=2984078 q=2663)
[94466.160485] Task dump for CPU 1:
[94466.160494] gem_concurrent_ R  running task        0 22751  22747 0x0000000a
[94466.160508]  ffffffff81a2e4c0 ffff88027fd03e70 ffffffff81097ac9
0000000000000001
[94466.160526]  ffffffff81a2e4c0 ffff88027fd03e88 ffffffff81099c37
0000000000000002
[94466.160546]  ffff88027fd03eb8 ffffffff810b9cee ffff88027fd157c0
ffffffff81a2e4c0
[94466.160563] Call Trace:
[94466.160571]  <IRQ>  [<ffffffff81097ac9>] sched_show_task+0xa9/0x110
[94466.160592]  [<ffffffff81099c37>] dump_cpu_task+0x37/0x40
[94466.160601]  [<ffffffff810b9cee>] rcu_dump_cpu_stacks+0x8e/0xe0
[94466.160611]  [<ffffffff810bd9b8>] rcu_check_callbacks+0x4c8/0x770
[94466.160621]  [<ffffffff810c1239>] update_process_times+0x39/0x60
[94466.160632]  [<ffffffff810cdc0b>] tick_periodic+0x2b/0x70
[94466.160641]  [<ffffffff810cdc75>] tick_handle_periodic+0x25/0x70
[94466.160652]  [<ffffffff81034ab8>] local_apic_timer_interrupt+0x38/0x60
[94466.160664]  [<ffffffff8147e15d>] smp_apic_timer_interrupt+0x3d/0x50
[94466.160675]  [<ffffffff8147c94c>] apic_timer_interrupt+0x7c/0x90
[94466.160682]  <EOI>  [<ffffffff8134f643>] ?
drm_prime_remove_buf_handle_locked+0x33/0x80
[94466.160703]  [<ffffffff8136f00c>] ? dma_buf_put+0x1c/0x40
[94466.160713]  [<ffffffff813366f8>] drm_gem_object_release_handle+0x88/0xa0
[94466.160724]  [<ffffffff8127ec7f>] idr_for_each+0x9f/0xe0
[94466.160733]  [<ffffffff81336670>] ?
drm_gem_object_handle_unreference_unlocked+0x110/0x110
[94466.160746]  [<ffffffff81336d60>] drm_gem_release+0x20/0x30
[94466.160755]  [<ffffffff81335bd3>] drm_release+0x3e3/0x4d0
[94466.160766]  [<ffffffff8115dfce>] __fput+0xce/0x1c0
[94466.160775]  [<ffffffff8115e0fe>] ____fput+0xe/0x10
[94466.160784]  [<ffffffff8108b203>] task_work_run+0x73/0x90
[94466.160794]  [<ffffffff81073217>] do_exit+0x367/0xa80
[94466.160885]  [<ffffffff8117a864>] ? mntput+0x24/0x40
[94466.160895]  [<ffffffff810745d3>] do_group_exit+0x43/0xb0
[94466.160904]  [<ffffffff81074654>] SyS_exit_group+0x14/0x20
[94466.160913]  [<ffffffff8147bc97>] entry_SYSCALL_64_fastpath+0x12/0x66

and makes every dmabuf test orders of magnitude slower than it should be.

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