| author |  Matthew Lugg <mlugg@mlugg.co.uk> 2026-01-06 10:50:45+00:00 |
| committer | Matthew Lugg <mlugg@mlugg.co.uk> 2026-01-06 10:50:45+00:00 |
| log | 111165513156d5732d85e5ccb52b9d8bded41ffa |
| tree | d92c2b23c5a611a3383cc4fe3fd441d1724fe831 |
| parent | 9d08eba2e111e96133b51c14aca7dc071920b6d2 |
| signature |  Commit is signed but in an unrecognized format. |
std: block cancelation in default panic and segfault handlers
It doesn't make any sense for a task to be canceled while it's
panicking.
As a happy accident, this also solves some cases where safety panics in
`Io.Threaded` would cause stack traces not to print due to invalid
thread-local state: when cancelation is blocked, `Io.Threaded` doesn't
consult said thread-local state at all. For instance, try inserting a
panic just after a call to `Syscall.start()` in `Io.Threaded`, and then
call the `Io` function in question from a `concurrent` task. Before this
PR, the stack trace fails to print, because the panic handler sees the
thread-local cancelation state in an unexpected state, leading to a
recursive panic. After this PR, the stack trace prints fine.1 files changed, 8 insertions(+), 0 deletions(-)
lib- std
lib/std/debug.zig+8
| ... | ... | @@ -532,6 +532,10 @@ pub fn defaultPanic(msg: []const u8, first_trace_addr: ?usize) noreturn { |
| 532 | 532 | else => {}, |
| 533 | 533 | } |
| 534 | 534 | |
| 535 | // Don't try to cancel during a panic. No need to re-enable cancelation, | |
| 536 | // because the panic handler doesn't return. | |
| 537 | _ = std.Options.debug_io.swapCancelProtection(.blocked); | |
| 538 | ||
| 535 | 539 | if (enable_segfault_handler) { |
| 536 | 540 | // If a segfault happens while panicking, we want it to actually segfault, not trigger |
| 537 | 541 | // the handler. |
| ... | ... | @@ -1533,6 +1537,10 @@ fn handleSegfault(addr: ?usize, name: []const u8, opt_ctx: ?CpuContextPtr) noret |
| 1533 | 1537 | } |
| 1534 | 1538 | |
| 1535 | 1539 | pub fn defaultHandleSegfault(addr: ?usize, name: []const u8, opt_ctx: ?CpuContextPtr) noreturn { |
| 1540 | // Don't try to cancel during a segfault. No need to re-enable cancelation, | |
| 1541 | // because the segfault handler doesn't return. | |
| 1542 | _ = std.Options.debug_io.swapCancelProtection(.blocked); | |
| 1543 | ||
| 1536 | 1544 | // There is very similar logic to the following in `defaultPanic`. |
| 1537 | 1545 | switch (panic_stage) { |
| 1538 | 1546 | 0 => { |