[go] runtime: allow Stack to traceback goroutines in syscall _Grunning window
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Michael Knyszek (Gerrit)
Oct 30, 2025, 4:32:55 PM (7 days ago) Oct 30
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Michael Pratt (Gerrit)
Nov 3, 2025, 5:09:10 PM (3 days ago) Nov 3
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Michael Knyszek (Gerrit)
Nov 3, 2025, 5:39:00 PM (3 days ago) Nov 3
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Michael Knyszek (Gerrit)
Nov 3, 2025, 5:54:17 PM (3 days ago) Nov 3
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Change information
Commit message:
runtime: allow Stack to traceback goroutines in syscall _Grunning window
net/http/cgi.TestCopyError calls runtime.Stack to take a stack trace of
all goroutines, and searches for a specific line in that stack trace.
It currently sometimes fails because it encounters the goroutine its
looking for in the small window where a goroutine might be in _Grunning
while in a syscall, introduced in CL 646198. In that case, the traceback
will give up, failing to print the stack TestCopyError is expecting.
This represents a general regression, since previously runtime.Stack
could never fail to take a goroutine's stack; giving up was only
possible in fatal panic cases.
Fix this the same way we fixed goroutine profiles: allow the stack trace
to proceed if the g's syscallsp != 0. This is safe in any
stop-the-world-related context, because syscallsp won't be mutated while
the goroutine fails to acquire a P, and thus fails to fully exit the
syscall context. This also means the stack below syscallsp won't be
mutated, and thus taking a traceback is also safe.
Fixes #66639.
Change-Id: Ie6f4b0661d9f8df02c9b8434e99bc95f26fe5f0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/716680
Reviewed-by: Michael Pratt <mpr...@google.com>
LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>
Files:
- M src/runtime/traceback.go
Change size: S
Delta: 1 file changed, 10 insertions(+), 1 deletion(-)
Branch: refs/heads/master
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