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    b2441318
    License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
    Greg Kroah-Hartman authored
    
    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: default avatarKate Stewart <kstewart@linuxfoundation.org>
    Reviewed-by: default avatarPhilippe Ombredanne <pombredanne@nexb.com>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    b2441318
    History
    License cleanup: add SPDX GPL-2.0 license identifier to files with no license
    Greg Kroah-Hartman authored
    
    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: default avatarKate Stewart <kstewart@linuxfoundation.org>
    Reviewed-by: default avatarPhilippe Ombredanne <pombredanne@nexb.com>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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osq_lock.c 5.60 KiB
// SPDX-License-Identifier: GPL-2.0
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/osq_lock.h>

/*
 * An MCS like lock especially tailored for optimistic spinning for sleeping
 * lock implementations (mutex, rwsem, etc).
 *
 * Using a single mcs node per CPU is safe because sleeping locks should not be
 * called from interrupt context and we have preemption disabled while
 * spinning.
 */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_node, osq_node);

/*
 * We use the value 0 to represent "no CPU", thus the encoded value
 * will be the CPU number incremented by 1.
 */
static inline int encode_cpu(int cpu_nr)
{
	return cpu_nr + 1;
}

static inline int node_cpu(struct optimistic_spin_node *node)
{
	return node->cpu - 1;
}

static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
{
	int cpu_nr = encoded_cpu_val - 1;

	return per_cpu_ptr(&osq_node, cpu_nr);
}

/*
 * Get a stable @node->next pointer, either for unlock() or unqueue() purposes.
 * Can return NULL in case we were the last queued and we updated @lock instead.
 */
static inline struct optimistic_spin_node *
osq_wait_next(struct optimistic_spin_queue *lock,
	      struct optimistic_spin_node *node,
	      struct optimistic_spin_node *prev)
{
	struct optimistic_spin_node *next = NULL;
	int curr = encode_cpu(smp_processor_id());
	int old;

	/*
	 * If there is a prev node in queue, then the 'old' value will be
	 * the prev node's CPU #, else it's set to OSQ_UNLOCKED_VAL since if
	 * we're currently last in queue, then the queue will then become empty.
	 */
	old = prev ? prev->cpu : OSQ_UNLOCKED_VAL;

	for (;;) {
		if (atomic_read(&lock->tail) == curr &&
		    atomic_cmpxchg_acquire(&lock->tail, curr, old) == curr) {
			/*
			 * We were the last queued, we moved @lock back. @prev
			 * will now observe @lock and will complete its
			 * unlock()/unqueue().
			 */
			break;
		}

		/*
		 * We must xchg() the @node->next value, because if we were to
		 * leave it in, a concurrent unlock()/unqueue() from
		 * @node->next might complete Step-A and think its @prev is
		 * still valid.
		 *
		 * If the concurrent unlock()/unqueue() wins the race, we'll
		 * wait for either @lock to point to us, through its Step-B, or
		 * wait for a new @node->next from its Step-C.
		 */
		if (node->next) {
			next = xchg(&node->next, NULL);
			if (next)
				break;
		}

		cpu_relax();
	}

	return next;
}

bool osq_lock(struct optimistic_spin_queue *lock)
{
	struct optimistic_spin_node *node = this_cpu_ptr(&osq_node);
	struct optimistic_spin_node *prev, *next;
	int curr = encode_cpu(smp_processor_id());
	int old;

	node->locked = 0;
	node->next = NULL;
	node->cpu = curr;

	/*
	 * We need both ACQUIRE (pairs with corresponding RELEASE in
	 * unlock() uncontended, or fastpath) and RELEASE (to publish
	 * the node fields we just initialised) semantics when updating
	 * the lock tail.
	 */
	old = atomic_xchg(&lock->tail, curr);
	if (old == OSQ_UNLOCKED_VAL)
		return true;

	prev = decode_cpu(old);
	node->prev = prev;

	/*
	 * osq_lock()			unqueue
	 *
	 * node->prev = prev		osq_wait_next()
	 * WMB				MB
	 * prev->next = node		next->prev = prev // unqueue-C
	 *
	 * Here 'node->prev' and 'next->prev' are the same variable and we need
	 * to ensure these stores happen in-order to avoid corrupting the list.
	 */
	smp_wmb();

	WRITE_ONCE(prev->next, node);

	/*
	 * Normally @prev is untouchable after the above store; because at that
	 * moment unlock can proceed and wipe the node element from stack.
	 *
	 * However, since our nodes are static per-cpu storage, we're
	 * guaranteed their existence -- this allows us to apply
	 * cmpxchg in an attempt to undo our queueing.
	 */

	while (!READ_ONCE(node->locked)) {
		/*
		 * If we need to reschedule bail... so we can block.
		 * Use vcpu_is_preempted() to avoid waiting for a preempted
		 * lock holder:
		 */
		if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
			goto unqueue;

		cpu_relax();
	}
	return true;

unqueue:
	/*
	 * Step - A  -- stabilize @prev
	 *
	 * Undo our @prev->next assignment; this will make @prev's
	 * unlock()/unqueue() wait for a next pointer since @lock points to us
	 * (or later).
	 */

	for (;;) {
		if (prev->next == node &&
		    cmpxchg(&prev->next, node, NULL) == node)
			break;

		/*
		 * We can only fail the cmpxchg() racing against an unlock(),
		 * in which case we should observe @node->locked becomming
		 * true.
		 */
		if (smp_load_acquire(&node->locked))
			return true;

		cpu_relax();

		/*
		 * Or we race against a concurrent unqueue()'s step-B, in which
		 * case its step-C will write us a new @node->prev pointer.
		 */
		prev = READ_ONCE(node->prev);
	}

	/*
	 * Step - B -- stabilize @next
	 *
	 * Similar to unlock(), wait for @node->next or move @lock from @node
	 * back to @prev.
	 */

	next = osq_wait_next(lock, node, prev);
	if (!next)
		return false;

	/*
	 * Step - C -- unlink
	 *
	 * @prev is stable because its still waiting for a new @prev->next
	 * pointer, @next is stable because our @node->next pointer is NULL and
	 * it will wait in Step-A.
	 */

	WRITE_ONCE(next->prev, prev);
	WRITE_ONCE(prev->next, next);

	return false;
}

void osq_unlock(struct optimistic_spin_queue *lock)
{
	struct optimistic_spin_node *node, *next;
	int curr = encode_cpu(smp_processor_id());
	/*
	 * Fast path for the uncontended case.
	 */
	if (likely(atomic_cmpxchg_release(&lock->tail, curr,
					  OSQ_UNLOCKED_VAL) == curr))
		return;

	/*
	 * Second most likely case.
	 */
	node = this_cpu_ptr(&osq_node);
	next = xchg(&node->next, NULL);
	if (next) {
		WRITE_ONCE(next->locked, 1);
		return;
	}

	next = osq_wait_next(lock, node, NULL);
	if (next)
		WRITE_ONCE(next->locked, 1);
}