<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> <style type="text/css" style="display:none;"></style> </head> <body dir="ltr"> <div id="divtagdefaultwrapper" style="font-size:12pt;color:#000000;font-family:Calibri,Helvetica,sans-serif;" dir="ltr"> <p style="margin-top:0;margin-bottom:0"></p> <div style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 16px;"> <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> <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;"> 1) considering below sequence:</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_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 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;"> <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, EmojiFont; font-size: 16px;"> 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 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; 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> <br> <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> <br> <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> <br> <div> <span style="color: #dcdcaa;">dma_fence_put</span>(old_fence);</div> <div> <span style="color: #c586c0;">return</span>;</div> <div> }</div> <br> <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> <p></p> </div> <hr style="display:inline-block;width:98%" tabindex="-1"> <div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Liu, Monk<br> <b>Sent:</b> Tuesday, March 6, 2018 5:45:19 PM<br> <b>To:</b> dri-devel@lists.freedesktop.org; Chris Wilson; Koenig, Christian<br> <b>Subject:</b> reservation questions </font> <div> </div> </div> <style type="text/css" style="display:none">  </style> <div dir="ltr"> <div id="x_divtagdefaultwrapper" dir="ltr" style="font-size:12pt; color:#000000; font-family:Calibri,Helvetica,sans-serif"> <p style="margin-top:0; margin-bottom:0"></p> <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></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"> <br> <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> <p></p> </div> </div> </body> </html>