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logind: set session->started before seat_read_active_vt() call

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session_start() calls seat_read_active_vt() before setting
s->started = true. seat_read_active_vt() can reach
seat_triggered_uevents_done() synchronously via:

  seat_active_vt_changed -> seat_set_active -> seat_trigger_devices
  -> seat_triggered_uevents_done

When seat_trigger_devices() produces no pending uevents,
seat_triggered_uevents_done() runs in the same call stack as
session_start() and tests session->started before the assignment
further down. The check fails, session_device_resume_all() is
skipped, and the compositor never receives DRM master.

Set started before seat_read_active_vt() so the gate sees the
correct value, and document the ordering constraint at the call
site to prevent regression.

Reproducible with greetd plus a Wayland compositor on the same VT
on kernel 6.19+.

Fixes: #41562
Signed-off-by: countgitmick <263313427+countgitmick@users.noreply.github.com>
This commit is contained in:
countgitmick
2026-04-09 00:53:03 -07:00
committed by Lennart Poettering
parent 001c5dfdf5
commit ce043cdfdb
1 changed files with 5 additions and 2 deletions
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7
src/login/logind-session.c
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@@ -923,11 +923,14 @@ int session_start(Session *s, sd_bus_message *properties, sd_bus_error *error) {
if (!dual_timestamp_is_set(&s->timestamp))
dual_timestamp_now(&s->timestamp);
/* Must be set before seat_read_active_vt(); the activation it
* triggers reaches seat_triggered_uevents_done() synchronously
* and gates session_device_resume_all() on s->started. */
s->started = true;
if (s->seat)
seat_read_active_vt(s->seat);
s->started = true;
user_elect_display(s->user);
/* Save data */