linux/kernel/locking/lockdep_internals.h, branch v5.4

locking/lockdep: Report more stack trace statistics

2019-07-25T13:43:28Z

Report the number of stack traces and the number of stack trace hash chains. These two numbers are useful because these allow to estimate the number of stack trace hash collisions. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Cc: Will Deacon Link: https://lkml.kernel.org/r/20190722182443.216015-5-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Reduce space occupied by stack traces

2019-07-25T13:43:27Z

Although commit 669de8bda87b ("kernel/workqueue: Use dynamic lockdep keys for workqueues") unregisters dynamic lockdep keys when a workqueue is destroyed, a side effect of that commit is that all stack traces associated with the lockdep key are leaked when a workqueue is destroyed. Fix this by storing each unique stack trace once. Other changes in this patch are: - Use NULL instead of { .nr_entries = 0 } to represent 'no trace'. - Store a pointer to a stack trace in struct lock_class and struct lock_list instead of storing 'nr_entries' and 'offset'. This patch avoids that the following program triggers the "BUG: MAX_STACK_TRACE_ENTRIES too low!" complaint: #include #include int main() { for (;;) { int fd = open("/dev/infiniband/rdma_cm", O_RDWR); close(fd); } } Suggested-by: Peter Zijlstra Reported-by: Eric Biggers Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Waiman Long Cc: Will Deacon Cc: Yuyang Du Link: https://lkml.kernel.org/r/20190722182443.216015-4-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Make it clear that what lock_class::key points at is not modified

2019-07-25T13:43:26Z

This patch does not change the behavior of the lockdep code. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Cc: Will Deacon Link: https://lkml.kernel.org/r/20190722182443.216015-2-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: increase size of counters for lockdep statistics

2019-06-25T08:17:08Z

When system has been running for a long time, signed integer counters are not enough for some lockdep statistics. Using unsigned long counters can satisfy the requirement. Besides, most of lockdep statistics are unsigned. It is better to use unsigned int instead of int. Remove unused variables. - max_recursion_depth - nr_cyclic_check_recursions - nr_find_usage_forwards_recursions - nr_find_usage_backwards_recursions Signed-off-by: Kobe Wu Signed-off-by: Peter Zijlstra (Intel) Cc: Cc: Cc: Eason Lin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: https://lkml.kernel.org/r/1561365348-16050-1-git-send-email-kobe-cp.wu@mediatek.com Signed-off-by: Ingo Molnar

locking/lockdep: Test all incompatible scenarios at once in check_irq_usage()

2019-04-29T06:29:20Z

check_prev_add_irq() tests all incompatible scenarios one after the other while adding a lock (@next) to a tree dependency (@prev): LOCK_USED_IN_HARDIRQ vs LOCK_ENABLED_HARDIRQ LOCK_USED_IN_HARDIRQ_READ vs LOCK_ENABLED_HARDIRQ LOCK_USED_IN_SOFTIRQ vs LOCK_ENABLED_SOFTIRQ LOCK_USED_IN_SOFTIRQ_READ vs LOCK_ENABLED_SOFTIRQ Also for these four scenarios, we must at least iterate the @prev backward dependency. Then if it matches the relevant LOCK_USED_* bit, we must also iterate the @next forward dependency. Therefore in the best case we iterate 4 times, in the worst case 8 times. A different approach can let us divide the number of branch iterations by 4: 1) Iterate through @prev backward dependencies and accumulate all the IRQ uses in a single mask. In the best case where the current lock hasn't been used in IRQ, we stop here. 2) Iterate through @next forward dependencies and try to find a lock whose usage is exclusive to the accumulated usages gathered in the previous step. If we find one (call it @lockA), we have found an incompatible use, otherwise we stop here. Only bad locking scenario go further. So a sane verification stop here. 3) Iterate again through @prev backward dependency and find the lock whose usage matches @lockA in term of incompatibility. Call that lock @lockB. 4) Report the incompatible usages of @lockA and @lockB If no incompatible use is found, the verification never goes beyond step 2 which means at most two iterations. The following compares the execution measurements of the function check_prev_add_irq(): Number of calls | Avg (ns) | Stdev (ns) | Total time (ns) ------------------------------------------------------------------------ Mainline 8452 | 2652 | 11962 | 22415143 This patch 8452 | 1518 | 7090 | 12835602 Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: https://lkml.kernel.org/r/20190402160244.32434-5-frederic@kernel.org Signed-off-by: Ingo Molnar

locking/lockdep: Generate LOCKF_ bit composites

2019-04-18T10:50:18Z

Instead of open-coding the bitmasks, generate them using the lockdep_states.h header. This prepares for additional states, which would make the manual masks tedious and error prone. Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Signed-off-by: Ingo Molnar

locking/lockdep: Introduce lockdep_next_lockchain() and lock_chain_count()

2019-02-28T06:55:44Z

This patch does not change any functionality but makes the next patch in this series easier to read. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Johannes Berg Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Cc: Will Deacon Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20190214230058.196511-14-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Provide enum lock_usage_bit mask names

2019-01-21T10:18:56Z

It makes the code more self-explanatory and tells throughout the code what magic number refers to: - state (Hardirq/Softirq) - direction (used in or enabled above state) - read or write We can even remove some comments that were compensating for the lack of those constant names. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: https://lkml.kernel.org/r/1545973321-24422-3-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar

locking/lockdep: Make class->ops a percpu counter and move it under CONFIG_DEBUG_LOCKDEP=y

2018-10-09T07:56:33Z

A sizable portion of the CPU cycles spent on the __lock_acquire() is used up by the atomic increment of the class->ops stat counter. By taking it out from the lock_class structure and changing it to a per-cpu per-lock-class counter, we can reduce the amount of cacheline contention on the class structure when multiple CPUs are trying to acquire locks of the same class simultaneously. To limit the increase in memory consumption because of the percpu nature of that counter, it is now put back under the CONFIG_DEBUG_LOCKDEP config option. So the memory consumption increase will only occur if CONFIG_DEBUG_LOCKDEP is defined. The lock_class structure, however, is reduced in size by 16 bytes on 64-bit archs after ops removal and a minor restructuring of the fields. This patch also fixes a bug in the increment code as the counter is of the 'unsigned long' type, but atomic_inc() was used to increment it. Signed-off-by: Waiman Long Acked-by: Peter Zijlstra Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: http://lkml.kernel.org/r/d66681f3-8781-9793-1dcf-2436a284550b@redhat.com Signed-off-by: Ingo Molnar

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

2017-11-02T10:10:55Z

Many source files in the tree are missing licensing information, which makes it harder for compliance tools to determine the correct license. By default all files without license information are under the default license of the kernel, which is GPL version 2. Update the files which contain no license information with the 'GPL-2.0' SPDX license identifier. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. How this work was done: Patches were generated and checked against linux-4.14-rc6 for a subset of the use cases: - file had no licensing information it it. - file was a */uapi/* one with no licensing information in it, - file was a */uapi/* one with existing licensing information, Further patches will be generated in subsequent months to fix up cases where non-standard license headers were used, and references to license had to be inferred by heuristics based on keywords. The analysis to determine which SPDX License Identifier to be applied to a file was done in a spreadsheet of side by side results from of the output of two independent scanners (ScanCode & Windriver) producing SPDX tag:value files created by Philippe Ombredanne. Philippe prepared the base worksheet, and did an initial spot review of a few 1000 files. The 4.13 kernel was the starting point of the analysis with 60,537 files assessed. Kate Stewart did a file by file comparison of the scanner results in the spreadsheet to determine which SPDX license identifier(s) to be applied to the file. She confirmed any determination that was not immediately clear with lawyers working with the Linux Foundation. Criteria used to select files for SPDX license identifier tagging was: - Files considered eligible had to be source code files. - Make and config files were included as candidates if they contained >5 lines of source - File already had some variant of a license header in it (even if <5 lines). All documentation files were explicitly excluded. The following heuristics were used to determine which SPDX license identifiers to apply. - when both scanners couldn't find any license traces, file was considered to have no license information in it, and the top level COPYING file license applied. For non */uapi/* files that summary was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 11139 and resulted in the first patch in this series. If that file was a */uapi/* path one, it was "GPL-2.0 WITH Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 WITH Linux-syscall-note 930 and resulted in the second patch in this series. - if a file had some form of licensing information in it, and was one of the */uapi/* ones, it was denoted with the Linux-syscall-note if any GPL family license was found in the file or had no licensing in it (per prior point). Results summary: SPDX license identifier # files ---------------------------------------------------|------ GPL-2.0 WITH Linux-syscall-note 270 GPL-2.0+ WITH Linux-syscall-note 169 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17 LGPL-2.1+ WITH Linux-syscall-note 15 GPL-1.0+ WITH Linux-syscall-note 14 ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5 LGPL-2.0+ WITH Linux-syscall-note 4 LGPL-2.1 WITH Linux-syscall-note 3 ((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3 ((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1 and that resulted in the third patch in this series. - when the two scanners agreed on the detected license(s), that became the concluded license(s). - when there was disagreement between the two scanners (one detected a license but the other didn't, or they both detected different licenses) a manual inspection of the file occurred. - In most cases a manual inspection of the information in the file resulted in a clear resolution of the license that should apply (and which scanner probably needed to revisit its heuristics). - When it was not immediately clear, the license identifier was confirmed with lawyers working with the Linux Foundation. - If there was any question as to the appropriate license identifier, the file was flagged for further research and to be revisited later in time. In total, over 70 hours of logged manual review was done on the spreadsheet to determine the SPDX license identifiers to apply to the source files by Kate, Philippe, Thomas and, in some cases, confirmation by lawyers working with the Linux Foundation. Kate also obtained a third independent scan of the 4.13 code base from FOSSology, and compared selected files where the other two scanners disagreed against that SPDX file, to see if there was new insights. The Windriver scanner is based on an older version of FOSSology in part, so they are related. Thomas did random spot checks in about 500 files from the spreadsheets for the uapi headers and agreed with SPDX license identifier in the files he inspected. For the non-uapi files Thomas did random spot checks in about 15000 files. In initial set of patches against 4.14-rc6, 3 files were found to have copy/paste license identifier errors, and have been fixed to reflect the correct identifier. Additionally Philippe spent 10 hours this week doing a detailed manual inspection and review of the 12,461 patched files from the initial patch version early this week with: - a full scancode scan run, collecting the matched texts, detected license ids and scores - reviewing anything where there was a license detected (about 500+ files) to ensure that the applied SPDX license was correct - reviewing anything where there was no detection but the patch license was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied SPDX license was correct This produced a worksheet with 20 files needing minor correction. This worksheet was then exported into 3 different .csv files for the different types of files to be modified. These .csv files were then reviewed by Greg. Thomas wrote a script to parse the csv files and add the proper SPDX tag to the file, in the format that the file expected. This script was further refined by Greg based on the output to detect more types of files automatically and to distinguish between header and source .c files (which need different comment types.) Finally Greg ran the script using the .csv files to generate the patches. Reviewed-by: Kate Stewart Reviewed-by: Philippe Ombredanne Reviewed-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman