RESOLVED FIXED314131
[Site Isolation] Only reuse target back/forward item's process when navigating the main frame 
https://bugs.webkit.org/show_bug.cgi?id=314131
Summary [Site Isolation] Only reuse target back/forward item's process when navigatin...
Basuke Suzuki
Reported 2026-05-05 15:34:39 PDT
In WebProcessPool::processForNavigationInternal, when handling a back/forward navigation, the code looks up targetItem->lastProcessIdentifier() and reuses that process for any frame — including subframes. Under Site Isolation with multi-process BFCache enabled, subframe back/forward navigations can reach this code path. The target back/forward item's lastProcessIdentifier is always the main frame's process, so using it for a subframe navigation picks the wrong process. Guard the lastProcessIdentifier lookup with frame.isMainFrame() so only main-frame navigations take this path. Subframe back/forward navigations fall through to the normal process-selection logic, which selects the appropriate site-matched process for the subframe. Prep patch for rdar://173743733 (multi-process BFCache restoration under Site Isolation).
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Add attachment proposed patch, testcase, etc.
Basuke Suzuki
Comment 1 2026-05-05 16:45:54 PDT
<rdar://problem/176305015>
Basuke Suzuki
Comment 2 2026-05-05 16:46:10 PDT
Pull request: https://github.com/WebKit/WebKit/pull/64311
EWS
Comment 3 2026-05-06 14:17:25 PDT
Committed 312735@main (4fd10b14732e): <https://commits.webkit.org/312735@main> Reviewed commits have been landed. Closing PR #64311 and removing active labels.
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