2017-03-25 5:08 GMT+09:00 Dmitry Vyukov <dvyukov@xxxxxxxxxx>: > Add /sys/kernel/debug/fail_once file that allows failing 0-th, 1-st, 2-nd > and so on calls systematically. Excerpt from the added documentation: > > === > Write to this file of integer N makes N-th call in the current task fail > (N is 0-based). Read from this file returns a single char 'Y' or 'N' > that says if the fault setup with a previous write to this file was > injected or not, and disables the fault if it wasn't yet injected. > Note that this file enables all types of faults (slab, futex, etc). > This setting takes precedence over all other generic settings like > probability, interval, times, etc. But per-capability settings > (e.g. fail_futex/ignore-private) take precedence over it. > This feature is intended for systematic testing of faults in a single > system call. See an example below. > === The "/sys/kernel/debug/fail_once" contains per-task data. Should we introduce new per-task file like "/proc/<pid>/fail-nth" instead of adding a single global debugfs file? > Why adding new setting: > 1. Existing settings are global rather than per-task. > So parallel testing is not possible. > 2. attr->interval is close but it depends on attr->count > which is non reset to 0, so interval does not work as expected. > 3. Trying to model this with existing settings requires manipulations > of all of probability, interval, times, space, task-filter and > unexposed count and per-task make-it-fail files. > 4. Existing settings are per-failure-type, and the set of failure > types is potentially expanding. > 5. make-it-fail can't be changed by unprivileged user and aggressive > stress testing better be done from an unprivileged user. > Similarly, this would require opening the debugfs files to the > unprivileged user, as he would need to reopen at least times file > (not possible to pre-open before dropping privs). > > The proposed interface solves all of the above (see the example). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
