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charset="us-ascii"; Format="flowed" Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" On 2022-09-23 18:05, Eric Wong wrote: > Mathieu Desnoyers wrote: >> On 2022-09-23 13:55, Eric Wong wrote: >>> Mathieu Desnoyers wrote: >>>> On 2022-09-22 05:15, Eric Wong via lttng-dev wrote: >>>>> Hello, I'm using urcu-bp + rculfhash + call_rcu to implement >>>>> malloc instrumentation (via LD_PRELOAD) on an existing >>>>> single-threaded Perl codebase which uses Linux signalfd. >>>>> >>>>> signalfd depends on signals being blocked in all threads >>>>> of the process, otherwise threads with unblocked signals >>>>> can receive them and starve the signalfd. >>>>> >>>>> While some threads in URCU do block signals (e.g. workqueue >>>>> worker for rculfhash), the call_rcu thread and rculfhash >>>>> partition_resize_helper threads do not... >>>>> >>>>> Should all threads URCU creates block signals (aside from SIGRCU)? >>>> >>>> Yes, I think you are right. The SIGRCU signal is only needed for the >>>> urcu-signal flavor though. >>>> >>>> Would you like to submit a patch ? >>> >>> Sure. >>> >>> Is there a way to detect at runtime when urcu-signal is in use >>> so SIGRCU (SIGUSR1) doesn't get unblocked when using other flavors? >>> >>> I actually use SIGUSR1 in my signalfd-using codebase. >>> >>> I also want to remove cds_lfht_worker_init entirely since it's racy. >>> Signal blocking needs to be done in the parent before pthread_create >>> to avoid a window where the child has unblocked signals. >>> >>> Thanks. Anyways, this is my work-in-progress: >>> >> >> Perhaps with this on top of your wip patch ? The idea is to always block all >> signals before creating threads, and only unblock SIGRCU when registering a >> urcu-signal thread. (compile-tested only) > > Thanks, that makes sense. It passes: make check short_bench > > My original signalfd + urcu-bp case works well, too, with my > constructor workarounds reverted. (I ported our patches ported to > to 0.10.2 for Debian buster (oldstable)). > > I don't know if the existing test coverage is sufficient, > though. Waiting on regtest... Do you mind if I fold our 2 patches together with a Co-developed-by tag and use your Signed-off-by ? Then the question that will arise is whether this change is sufficiently self-contained that we can push it to stable branches, or if it's master branch material only. Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev