Re: [APC-DEV] [PATCH] APC signals + coredump shared memory unmapping

We have extremely bad experience with SEGV signal handlers seg faulting themselves and sending the server into an infinite loop and thus taking it down. I don't mind the patch, but we should make sure people understand the risks. -Rasmus Lucas Nealan wrote: > Hi, > > I would like to propose the attached patch against APC CVS HEAD. It provides > the configurable ability to trap coredump related signals and unmap the APC > shared memory segment while still calling any previously installed signal > handlers. This feature would be enabled via a new apc ini entry, > apc.coredump_unmap, which is defaulted to disabled. > > Although this will technically work in production environments the > functionality was engineered to solve a problem in shared development > environments that require a really large apc shm size. In these environments > when a coredump occurs in the SAPI, PHP or an extension the coredump file > mayb be many gigabytes. If enough of these are generated concurrently, > writing these large files may bring down a server. > > All signal handling is done through sigaction and will be compiled out if > autoconf HAVE_SIGACTION is not set (or it's overrided). The signal handling > also uses SA_SIGINFO in order to maintain the ability to call previously > registered handlers that also use this flag. > > Signal handlers are registered per child in module RINIT since SAPIs like > Apache may register their signal handlers after MINIT. Information about the > previous handlers is stored in a module static. I believe this will be safe > in ZTS builds since handlers will only be registered once in a non forking > mode. If requested I will move these into APC globals. > > As a note, although newer Linux kernels and other kernels may provide the > facility to ignore various types of shared memory when generating a > coredump, this type of setting does not allow the specificity that this > patch provides. For example someone running Apache/PHP with a large APC > cache may not want their mmaped Apache scoreboard excluded from their > coredump files. > > I've also made the patch available at the following url in case the > attachment is problematic: > > http://sizzo.org/~screen/patches/apc_signal_unmap.patch > > -lucas > > >