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runtime/pprof: inline frames may not use combined location [1.14 backport] #37447

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gopherbot opened this issue Feb 25, 2020 · 4 comments
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runtime/pprof: inline frames may not use combined location [1.14 backport] #37447

gopherbot opened this issue Feb 25, 2020 · 4 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
Milestone
Go1.14.1

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@gopherbot
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@hyangah requested issue #37446 to be considered for backport to the next 1.14 minor release.

@gopherbot please consider this for backport to 1.14, it's a regression.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Feb 25, 2020
@gopherbot gopherbot mentioned this issue Feb 25, 2020
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@gopherbot gopherbot added this to the Go1.14.1 milestone Feb 26, 2020
@hyangah
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hyangah commented Mar 6, 2020

@prattmic can you create a cherry-pick cl for this? I tried but I don't have the right permission to forge author. :-)

https://github.com/golang/go/wiki/MinorReleases#making-cherry-pick-cls

@gopherbot
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Change https://golang.org/cl/222762 mentions this issue: [release-branch.go1.14] runtime/pprof: expand final stack frame to avoid truncation

@dmitshur
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Approving as this is a serious issue and there is no reasonable workaround.

@dmitshur dmitshur added CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases labels Mar 10, 2020
@gopherbot
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Closed by merging 9c41c1d to release-branch.go1.14.

gopherbot pushed a commit that referenced this issue Mar 10, 2020
@prattmic @toothrot
[release-branch.go1.14] runtime/pprof: expand final stack frame to av…
9c41c1d 
…oid truncation

When generating stacks, the runtime automatically expands inline
functions to inline all inline frames in the stack. However, due to the
stack size limit, the final frame may be truncated in the middle of
several inline frames at the same location.

As-is, we assume that the final frame is a normal function, and emit and
cache a Location for it. If we later receive a complete stack frame, we
will first use the cached Location for the inlined function and then
generate a new Location for the "caller" frame, in violation of the
pprof requirement to merge inlined functions into the same Location.

As a result, we:

1. Nondeterministically may generate a profile with the different stacks
combined or split, depending on which is encountered first. This is
particularly problematic when performing a diff of profiles.

2. When split stacks are generated, we lose the inlining information.

We avoid both of these problems by performing a second expansion of the
last stack frame to recover additional inline frames that may have been
lost. This expansion is a bit simpler than the one done by the runtime
because we don't have to handle skipping, and we know that the last
emitted frame is not an elided wrapper, since it by definition is
already included in the stack.

Fixes #37447

Change-Id: If3ca2af25b21d252cf457cc867dd932f107d4c61
Reviewed-on: https://go-review.googlesource.com/c/go/+/221577
Run-TryBot: Michael Pratt <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
(cherry picked from commit fadbf74)
Reviewed-on: https://go-review.googlesource.com/c/go/+/222762
@tonyghita tonyghita mentioned this issue Mar 20, 2020
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@prattmic prattmic mentioned this issue Mar 26, 2020
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