On Sat, Mar 25, 2017 at 10:54 AM, Akinobu Mita <akinobu.mita@xxxxxxxxx> wrote: > 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? Mailed v2 that uses /proc/self/task/tid/fail-nth. >> 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>
