https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231793
--- Comment #5 from commit-h...@freebsd.org --- A commit references this bug: Author: mmacy Date: Fri Oct 5 05:55:57 UTC 2018 New revision: 339188 URL: https://svnweb.freebsd.org/changeset/base/339188 Log: hwpmc: Refactor sample ring buffer handling to fix races Refactor sample ring buffer ring handling to make it more robust to long running callchain collection handling r338112 introduced a (now fixed) regression that exposed a number of race conditions within the management of the sample buffers. This simplifies the handling and moves the decision to overwrite a callchain sample that has taken too long out of the NMI in to the hardlock handler. With this change the problem no longer shows up as a ring corruption but as the code spending all of its time in callchain collection. - Makes the producer / consumer index incrementing monotonic, making it easier (for me at least) to reason about. - Moves the decision to overwrite a sample from NMI context to interrupt context where we can enforce serialization. - Puts a time limit on waiting to collect a user callchain - putting a bound on head-of-line blocking causing samples to be dropped - Removes the flush routine which was previously needed to purge dangling references to the pmc from the sample buffers but now is only a source of a race condition on unload. Previously one could lock up or crash HEAD by running: pmcstat -S inst_retired.any_p -T and then hitting ^C After this change it is no longer possible. PR: 231793 Reviewed by: markj@ Approved by: re (gjb@) Differential Revision: https://reviews.freebsd.org/D17011 Changes: head/sys/dev/hwpmc/hwpmc_logging.c head/sys/dev/hwpmc/hwpmc_mod.c head/sys/sys/pmc.h head/sys/sys/pmckern.h -- You are receiving this mail because: You are the assignee for the bug. _______________________________________________ freebsd-bugs@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-bugs To unsubscribe, send any mail to "freebsd-bugs-unsubscr...@freebsd.org"
