68 lines
3.0 KiB
Diff
68 lines
3.0 KiB
Diff
From 422272d78399d5fb2fc340281611961fc7c528e7 Mon Sep 17 00:00:00 2001
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From: Alex Rousskov <rousskov@measurement-factory.com>
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Date: Thu, 23 Nov 2023 18:27:45 +0000
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Subject: [PATCH 4/7] Remove mem_hdr::freeDataUpto() assertion (#1562)
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stmem.cc:98: "lowestOffset () <= target_offset"
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....
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The assertion is conceptually wrong: The given target_offset parameter
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may have any value; that value does not have to correlate with mem_hdr
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state in any way. It is freeDataUpto() job to preserve nodes at or above
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the given offset and (arguably optionally) remove nodes below it, but
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the assertion does not actually validate that freeDataUpdo() did that.
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....
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The old mem_hdr::freeDataUpto() assertion incorrectly assumed that,
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after zero or more unneeded memory nodes were freed, the remaining
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memory area never starts after the given target_offset parameter. That
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assumption fails in at least two use cases, both using target_offset
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values that do not belong to any existing or future mem_hdr node:
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....
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1. target_offset is points to the left of the first node. freeDataUpto()
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correctly keeps all memory nodes in such calls, but then asserts. For
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example, calling freeDataUpto(0) when mem_hdr has bytes [100,199)
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triggers this incorrect assertion.
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....
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2. target_offset is in the gap between two nodes. For example, calling
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freeDataUpto(2000) when mem_hdr contains two nodes: [0,1000) and
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[3000,3003) will trigger this assertion (as happened in Bug 5309).
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Such gaps are very common for HTTP 206 responses with a Content-Range
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header because such responses often specify a range that does not
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start with zero and create a gap after the node(s) with HTTP headers.
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....
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Bugs notwithstanding, it is unlikely that relevant calls exist today,
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but they certainly could be added, especially when freeDataUpto() stops
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preserving the last unused node. The current "avoid change to [some
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unidentified] part of code" hoarding excuse should not last forever.
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....
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Prior to commit 122a6e3, Squid did not (frequently) assert in gap cases:
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Callers first give target_offset 0 (which results in freeDataUpto()
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doing nothing, keeping the header node(s)) and then they give
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target_offset matching the beginning of the first body node (which
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results in freeDataUpto() freeing the header nodes(s) and increasing
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lowerOffset() from zero to target_offset). A bug in commit 122a6e3
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lowered target_offset a bit, placing target_offset in the gap and
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triggering frequent (and incorrect) assertions (Bug 5309).
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Modified-by: Alex Burmashev <alexander.burmashev@oracle.com>
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Signed-off-by: Alex Burmashev <alexander.burmashev@oracle.com>
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---
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src/stmem.cc | 2 --
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1 file changed, 2 deletions(-)
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diff --git a/src/stmem.cc b/src/stmem.cc
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index d117c15..b627005 100644
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--- a/src/stmem.cc
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+++ b/src/stmem.cc
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@@ -95,8 +95,6 @@ mem_hdr::freeDataUpto(int64_t target_offset)
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break;
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}
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- assert (lowestOffset () <= target_offset);
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-
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return lowestOffset ();
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}
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--
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2.39.3
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