[Differential] [Commented On] D1711: Changes to the callout code to restore active semantics and also add a test-framework and test to validate thecallout code (and potentially for use by other tests).

[hselasky (Hans Petter Selasky)]

hselasky added a comment.

Hi,

rrs + hiren:

I think the problem is this:

In "_callout_stop_safe()" we sometimes exit having "cc_migration_cpu(cc, direct) = CPUBLOCK;". Now if a second call to "_callout_stop_safe()" happens before the pending callback has returned, which is using a mutex, we are deadlocked, because "_callout_stop_safe()" is called having the same lock locked which the callback needs to aquire aswell. Because the callout subsystem cannot aquire the mutex during the callback function, it can neither reach the migration code which resets the cc_migration_cpu() variable.

hiren: Can you backtrace all the softclock processes in your dump?

--HPS

REVISION DETAIL
  https://reviews.freebsd.org/D1711

To: rrs, gnn, rwatson, lstewart, jhb, kostikbel, sbruno, imp, adrian, hselasky
Cc: julian, hiren, jhb, kostikbel, emaste, delphij, neel, erj, freebsd-net