Bugzilla

Yes, we finally have the reasons why we're failing to write out the minidumps, see [this](https://crash-stats.mozilla.org/search/?release_channel=nightly&signature=%3DEMPTY%3A%20no%20crashing%20thread%20identified%3B%20EmptyMinidump&product=Firefox&version=102.0a1&date=%3E%3D2022-05-17T07%3A53%3A00.000Z&date=%3C2022-05-24T07%3A53%3A00.000Z&_facets=url&_facets=user_comments&_facets=install_time&_facets=version&_facets=address&_facets=moz_crash_reason&_facets=reason&_facets=build_id&_facets=platform_pretty_version&_facets=signature&_facets=dumper_error&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform#facet-dumper_error).

So out of the 34 recent crashes one thirds has a **No threads left to suspend (out of X)** error and another third has **Error during init phase: IO error for file /proc/<pid>/auxv: Permission denied (os error 13)** errors.

Regarding the first error it's probably happening because it's too late to write a minidump. I wonder if we could experiment with sending a `SIGSTOP` instead or use `ptrace()` with `PTRACE_ATTACH`. Regarding the latter error we can probably do away with the contents of the auxiliary vector and still write a mostly complete minidump. Additionally we might ptrace the auxiliary vector directly out of the crashed process if reading the corresponding /proc file fails. I'll file bugs for both.

Yes, we finally have the reasons why we're failing to write out the minidumps, see [this](https://crash-stats.mozilla.org/search/?release_channel=nightly&signature=%3DEMPTY%3A%20no%20crashing%20thread%20identified%3B%20EmptyMinidump&product=Firefox&version=102.0a1&date=%3E%3D2022-05-17T07%3A53%3A00.000Z&date=%3C2022-05-24T07%3A53%3A00.000Z&_facets=url&_facets=user_comments&_facets=install_time&_facets=version&_facets=address&_facets=moz_crash_reason&_facets=reason&_facets=build_id&_facets=platform_pretty_version&_facets=signature&_facets=dumper_error&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform#facet-dumper_error).

So out of the 34 recent crashes one thirds has a **No threads left to suspend (out of X)** error and another third has **Error during init phase: IO error for file /proc/<pid>/auxv: Permission denied (os error 13)** errors.

Regarding the first error it's probably happening because it's too late to write a minidump. I wonder if we could experiment with sending a `SIGSTOP` instead ~~or use ptrace() with PTRACE_ATTACH~~. Regarding the latter error we can probably do away with the contents of the auxiliary vector and still write a mostly complete minidump. Additionally we might ptrace the auxiliary vector directly out of the crashed process if reading the corresponding /proc file fails. I'll file bugs for both.

Edit: We already use PTRACE_ATTACH on every thread, sending it to the PID only stops that thread not the whole process but it's possible to SIGSTOP a process and then attach when the threads have already been stopped.