[libvirt] [PATCH 00/10] libxl: switch driver to use a single libxl_ctx

This series is a follow up to https://www.redhat.com/archives/libvir-list/2015-February/msg00024.html It goes a step further and changes the libxl driver to use one, driver-wide libxl_ctx. Currently the libxl driver has one driver-wide ctx for operations that are not domain-specific and a ctx for each domain. This approach was necessary back in the old Xen4.1 libxl days, but with the newer libxl it is more of a hinderance than benefit. Ian Jackson suggested moving to a single ctx while discussing some deadlocks and assertions encountered in the libxl driver when under load from tests such as OpenStack Tempest. Making such a change involves quite a bit of code movement. I've tried to split that up into a reviewable series, the result of which are the 9 patches that follow. I've ran this through all of my automated tests as well as some hacky tests I created to reproduce failures revealed by Tempest. One downside of moving to a single ctx is losing the per-domain log files. Currently, a single log stream can be associated with ctx, hence all logging from libxl will go to a single file. Ian is going to investigate possibilities to accommodate per-domain log files in libxl, but in the meantime folks using Xen are accustomed to a single log file from the xend days. I've been testing this series on xen-unstable and Xen 4.4.1 + commits 2ffeb5d7, 4b9143e4, 5a968257, 60ce518a, 66bff9fd, 77a1bf37, f49f9b41, 6b5a5bba, 93699882d, f1335f0d, and 8bc64413. Results are much better than before applying the series, but I do notice a stuck hypercall after many (hundreds) concurrent domain create/destroy operations. The single libxl_ctx is locked in the callpath, essentially deadlocking the driver. Thread 1 (Thread 0x7f0649a198c0 (LWP 2235)): 0 0x00007f0645272397 in ioctl () from /lib64/libc.so.6 1 0x00007f0645d8e353 in linux_privcmd_hypercall (xch=<optimized out>, h=<optimized out>, hypercall=<optimized out>) at xc_linux_osdep.c:134 2 0x00007f0645d854b8 in do_xen_hypercall (xch=xch@entry=0x7f0630039390, hypercall=hypercall@entry=0x7fffd53f80e0) at xc_private.c:249 3 0x00007f0645d86aa4 in do_sysctl (sysctl=sysctl@entry=0x7fffd53f8080, xch=xch@entry=0x7f0630039390) at xc_private.h:281 4 xc_sysctl (xch=xch@entry=0x7f0630039390, sysctl=sysctl@entry=0x7fffd53f8170) at xc_private.c:656 5 0x00007f0645d7bfbf in xc_domain_getinfolist (xch=0x7f0630039390, first_domain=first_domain@entry=119, max_domains=max_domains@entry=1, info=info@entry=0x7fffd53f8260) at xc_domain.c:382 6 0x00007f0645fabca6 in domain_death_xswatch_callback (egc=0x7fffd53f83f0, w=<optimized out>, wpath=<optimized out>, epath=<optimized out>) at libxl.c:1041 7 0x00007f0645fd75a8 in watchfd_callback (egc=0x7fffd53f83f0, ev=<optimized out>, fd=<optimized out>, events=<optimized out>, revents=<optimized out>) at libxl_event.c:515 8 0x00007f0645fd8ac3 in libxl_osevent_occurred_fd (ctx=<optimized out>, for_libxl=<optimized out>, fd=<optimized out>, events_ign=<optimized out>, revents_ign=<optimized out>) at libxl_event.c:1259 9 0x00007f063a23402c in libxlFDEventCallback (watch=454, fd=33, vir_events=1, fd_info=0x7f0608007e70) at libxl/libxl_driver.c:123 There is no hint in any logs or dmesg suggesting a cause for the stuck hypercall. Any suggestions for further debugging tips appreciated. Jim Fehlig (10): libxl: remove redundant calls to libxl_evdisable_domain_death libxl: use libxl_ctx passed to libxlConsoleCallback libxl: use driver-wide ctx in fd and timer event handling libxl: Move setup of child processing code to driver initialization libxl: move event registration to driver initialization libxl: use global libxl_ctx in event handler libxl: remove unnecessary libxlDomainEventsRegister libxl: make libxlDomainFreeMem static libxl: remove per-domain libxl_ctx libxl: change libxl log stream to ERROR log level src/libxl/libxl_conf.c | 2 +- src/libxl/libxl_domain.c | 438 ++++++--------------------------------- src/libxl/libxl_domain.h | 27 +-- src/libxl/libxl_driver.c | 484 +++++++++++++++++++++++++++++++------------- src/libxl/libxl_migration.c | 17 +- 5 files changed, 426 insertions(+), 542 deletions(-) -- 1.8.4.5