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<div class="moz-cite-prefix">Am 06.03.2018 um 10:56 schrieb Liu,
Monk:<br>
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<br class="Apple-interchange-newline">
<span style="color: rgb(255, 0, 0);">sorry, I have some
mistake in previous thread, correct it as followings.</span></div>
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<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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1) considering below sequence:</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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call reservation_object_add_shared_fence,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
now assume old->shared_count is now 3</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
call reservation_object_add_shared_fence,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
now assume old->shared_count is now 4,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
call reservation_object_reserve_shared,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
now obj->staged is new allocated, and its shared_max = 8,
but not</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
used by far.</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
call reservation_object_add_excl_fence,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
it set obj->fence->shared_count to 0, <b>and put all
shared fence from obj->fence without waiting signaling.</b></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
(this action looks inappropriate, I think at least before put
all those shared fences</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
we should dma_wait_fence() on them to make sure they are
signaled)</div>
</div>
</blockquote>
<br>
The exclusive fence replaces all shared fences, e.g. the exclusive
operation needs to wait for all shared fences before it can access
the protected object. Because of this we can drop all shared fences
when a new exclusive fence is set.<br>
<br>
<blockquote type="cite"
cite="mid:BLUPR12MB04490E071F145B33500AC75484D90@BLUPR12MB0449.namprd12.prod.outlook.com">
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<br>
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<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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call reservation_object_reserve_shared,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<b>this time obj->staged isn't NULL, and it is freed</b> (nothing
bad now</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
since obj->fence points to other place),</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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and obj->staged set to NULL,</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="color: rgb(0, 111, 201);">call
reservation_object_add_shared_fence,</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="color: rgb(0, 111, 201);">this time should going
through <b>reservation_object_add_shared_inplace</b>,</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="color: rgb(0, 111, 201);">since
old->shared_count is 1 now, during </span><span
style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px; color: rgb(0, 111, 201);"><b>reservation_object_add_shared_inplace</b>()</span></div>
</div>
</blockquote>
<br>
Why would old->shared_count be 1 now? As far as I can see it
should be zero.<br>
<br>
Christian.<br>
<br>
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cite="mid:BLUPR12MB04490E071F145B33500AC75484D90@BLUPR12MB0449.namprd12.prod.outlook.com">
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<div style="font-family: Calibri, Helvetica, sans-serif, serif,
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<span style="font-family: Calibri, Helvetica, sans-serif,
serif, EmojiFont; font-size: 16px; color: rgb(0, 111, 201);">it
would go through the shared list, but the fence in shared
list is now wild pointer:</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: Calibri, Helvetica, sans-serif,
serif, EmojiFont; font-size: 16px;">
<div style="color: rgb(212, 212, 212); background-color: rgb(30, 30, 30); font-family: "Droid Sans Mono", monospace, monospace, "Droid Sans Fallback"; font-size: 14px; line-height: 19px; white-space: pre;">
<div> <span style="color: #c586c0;">for</span> (i = <span style="color: #b5cea8;">
0</span>; i < fobj-><span style="color: #9cdcfe;">shared_count</span>; ++i) {</div>
<div> <span style="color: #569cd6;">struct</span> dma_fence *old_fence;</div>
<div><b> old_fence = <span style="color: #dcdcaa;">rcu_dereference_protected</span>(fobj-><span style="color: #9cdcfe;">shared</span>[i],</b></div>
<div><b> <span style="color: #dcdcaa;">reservation_object_held</span>(obj));</b></div>
<div> <span style="color: #c586c0;">if</span> (old_fence-><span style="color: #9cdcfe;">context</span> == fence-><span style="color: #9cdcfe;">context</span> &&</div>
<div> <span style="color: #dcdcaa;">dma_fence_is_later</span>(fence, old_fence)) {</div>
<div> <span style="color: #608b4e;">/* memory barrier is added by write_seqcount_begin */</span></div>
<div> <span style="color: #dcdcaa;">RCU_INIT_POINTER</span>(fobj-><span style="color: #9cdcfe;">shared</span>[i], fence);</div>
<div> <span style="color: #dcdcaa;">write_seqcount_end</span>(&obj-><span style="color: #9cdcfe;">seq</span>);</div>
<div> <span style="color: #dcdcaa;">preempt_enable</span>();</div>
<div> <span style="color: #dcdcaa;">dma_fence_put</span>(old_fence);</div>
<div> <span style="color: #c586c0;">return</span>;</div>
<div> }</div>
<div> <span style="color: #c586c0;">if</span> (!signaled && <span style="color: #dcdcaa;">
dma_fence_is_signaled</span>(old_fence)) {</div>
<div> signaled = old_fence;</div>
<div> signaled_idx = i;</div>
<div> }</div>
<div> }</div>
</div>
<br>
</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: Calibri, Helvetica, sans-serif,
serif, EmojiFont; font-size: 16px;">see that old_fence is
get from fobj, and fobj is from </span><span style="font-family: "Droid Sans Mono", monospace, monospace, "Droid Sans Fallback"; font-size: 14px; white-space: pre; color: rgb(0, 0, 0);">reservation_object_get_list(obj)</span><span style="background-color: rgb(30, 30, 30); color: rgb(0, 0, 0); font-family: "Droid Sans Mono", monospace, monospace, "Droid Sans Fallback"; font-size: 14px; white-space: pre;"></span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: "Droid Sans Mono", monospace, monospace, "Droid Sans Fallback"; font-size: 14px; white-space: pre; color: rgb(0, 0, 0);">in outside, which is obj->fence, and in add_excl_fence, all dma_fence in</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: "Droid Sans Mono", monospace, monospace, "Droid Sans Fallback"; font-size: 14px; white-space: pre; color: rgb(0, 0, 0);">obj->fence is already put.</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: Calibri, Helvetica, sans-serif,
serif, EmojiFont; font-size: 16px;"><br>
</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<span style="font-family: Calibri, Helvetica, sans-serif,
serif, EmojiFont; font-size: 16px;">/Monk</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif, serif,
EmojiFont; font-size: 16px;">
<b><br>
</b></div>
<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b> Liu,
Monk<br>
<b>Sent:</b> Tuesday, March 6, 2018 5:45:19 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:dri-devel@lists.freedesktop.org">dri-devel@lists.freedesktop.org</a>; Chris Wilson;
Koenig, Christian<br>
<b>Subject:</b> reservation questions </font>
<div> </div>
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<div>Hi Christian & Chris</div>
<div><br>
</div>
<div>two question regarding resv:</div>
<div><br>
</div>
<div>1) considering below sequence:</div>
<div><br>
</div>
<div>call reservation_object_add_shared_fence,</div>
<div>now assume old->shared_count is now 3</div>
<div>call reservation_object_add_shared_fence,</div>
<div>now assume old->shared_count is now 4,</div>
<div><br>
</div>
<div>call reservation_object_reserve_shared,</div>
<div>now obj->staged is new allocated, and its shared_max =
8, but not</div>
<div>used by far.</div>
<div><br>
</div>
<div>call reservation_object_add_excl_fence,</div>
<div>it set obj->fence->shared_count to 0, <b>and put
all shared fence from obj->fence without waiting
signaling.</b></div>
<div>(this action looks inappropriate, I think at least before
put all those shared fences</div>
<div>we should dma_wait_fence() on them to make sure they are
signaled)</div>
<div><br>
</div>
<div>call reservation_object_reserve_shared,</div>
<div><b>this time obj->staged isn't NULL, and it is freed</b>
(nothing bad now</div>
<div>since obj->fence points to other place),</div>
<div>and obj->staged set to NULL,</div>
<div><br>
</div>
<div>call reservation_object_add_shared_fence,</div>
<div>this time should going through
reservation_object_add_shared_inplace,</div>
<div><b>But BUG_ON(old->shared_count >=
old->shared_max) will hit !</b></div>
<div><b><br>
</b></div>
<div>This looks a design flaw in reservation object, shouldn't
we fix it ?</div>
<div><b><br>
</b></div>
<div><br>
</div>
<div>2) in add_excl_fence(), it simply set
old->shared_count to 0, and put all shared fences of old</div>
<div>is that correct? if excl fence is really exclusively
used, why we still consider both shared fence and</div>
<div>excl fence on wait_timeout_rcu() routine, see blew
description of this routine</div>
<div><br>
</div>
<div>
<div style="color:rgb(212,212,212); background-color:rgb(30,30,30); font-family:"Droid Sans Mono",monospace,monospace,"Droid Sans Fallback"; font-size:14px; line-height:19px; white-space:pre">
<div><span style="color:#608b4e">/**</span></div>
<div><span style="color:#608b4e">* reservation_object_wait_timeout_rcu - Wait on reservation's objects</span></div>
<div><span style="color:#608b4e">* shared and/or exclusive fences.</span></div>
<div><span style="color:#608b4e">* @obj: the reservation object</span></div>
<div><span style="color:#608b4e">* @wait_all: if true, wait on all fences, else wait on just exclusive fence</span></div>
<div><span style="color:#608b4e">* @intr: if true, do interruptible wait</span></div>
<div><span style="color:#608b4e">* @timeout: timeout value in jiffies or zero to return immediately</span></div>
<div><span style="color:#608b4e">*</span></div>
<div><span style="color:#608b4e">* RETURNS</span></div>
<div><span style="color:#608b4e">* Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or</span></div>
<div><span style="color:#608b4e">* greater than zer on success.</span></div>
<div><span style="color:#608b4e">*/</span></div>
<div><span style="color:#569cd6">long</span> <span style="color:#dcdcaa">reservation_object_wait_timeout_rcu</span>(<span style="color:#569cd6">struct</span> reservation_object *obj,</div>
<div> <span style="color:#569cd6">bool</span> wait_all, <span style="color:#569cd6">
bool</span> intr,</div>
<div> <span style="color:#569cd6">unsigned</span> <span style="color:#569cd6">
long</span> timeout)</div>
</div>
<br>
</div>
<div><span style="font-size:12pt"> </span><br>
</div>
<div><span style="font-size:12pt">thanks</span></div>
<div>/Monk</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<br>
</div>
</div>
</blockquote>
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