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2022-07-04lockref: remove unused 'lockref_get_or_lock()' functionLinus Torvalds1-1/+0
Looking at the conditional lock acquire functions in the kernel due to the new sparse support (see commit 4a557a5d1a61 "sparse: introduce conditional lock acquire function attribute"), it became obvious that the lockref code has a couple of them, but they don't match the usual naming convention for the other ones, and their return value logic is also reversed. In the other very similar places, the naming pattern is '*_and_lock()' (eg 'atomic_put_and_lock()' and 'refcount_dec_and_lock()'), and the function returns true when the lock is taken. The lockref code is superficially very similar to the refcount code, only with the special "atomic wrt the embedded lock" semantics. But instead of the '*_and_lock()' naming it uses '*_or_lock()'. And instead of returning true in case it took the lock, it returns true if it *didn't* take the lock. Now, arguably the reflock code is quite logical: it really is a "either decrement _or_ lock" kind of situation - and the return value is about whether the operation succeeded without any special care needed. So despite the similarities, the differences do make some sense, and maybe it's not worth trying to unify the different conditional locking primitives in this area. But while looking at this all, it did become obvious that the 'lockref_get_or_lock()' function hasn't actually had any users for almost a decade. The only user it ever had was the shortlived 'd_rcu_to_refcount()' function, and it got removed and replaced with 'lockref_get_not_dead()' back in 2013 in commits 0d98439ea3c6 ("vfs: use lockred 'dead' flag to mark unrecoverably dead dentries") and e5c832d55588 ("vfs: fix dentry RCU to refcounting possibly sleeping dput()") In fact, that single use was removed less than a week after the whole function was introduced in commit b3abd80250c1 ("lockref: add 'lockref_get_or_lock() helper") so this function has been around for a decade, but only had a user for six days. Let's just put this mis-designed and unused function out of its misery. We can think about the naming and semantic oddities of the remaining 'lockref_put_or_lock()' later, but at least that function has users. And while the naming is different and the return value doesn't match, that function matches the whole '{atomic,refcount}_dec_and_test()' pattern much better (ie the magic happens when the count goes down to zero, not when it is incremented from zero). Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-04-12lockref: Add lockref_put_not_zeroAndreas Gruenbacher1-0/+1
Put a lockref unless the lockref is dead or its count would become zero. This is the same as lockref_put_or_lock except that the lock is never left held. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
2018-02-07lib/lockref: __lockref_is_dead can be booleanYaowei Bai1-1/+1
Make __lockref_is_dead return bool due to this function only using either true or false as its return value. No functional change. Link: http://lkml.kernel.org/r/1513266622-15860-3-git-send-email-baiyaowei@cmss.chinamobile.com Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-02License cleanup: add SPDX GPL-2.0 license identifier to files with no licenseGreg Kroah-Hartman1-0/+1
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 <kstewart@linuxfoundation.org> Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2015-01-26dcache: let the dentry count go down to zero without taking d_lockLinus Torvalds1-1/+2
We can be more aggressive about this, if we are clever and careful. This is subtle. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-12-21mm: do not allocate page->ptl dynamically, if spinlock_t fits to longKirill A. Shutemov1-1/+1
In struct page we have enough space to fit long-size page->ptl there, but we use dynamically-allocated page->ptl if size(spinlock_t) is larger than sizeof(int). It hurts 64-bit architectures with CONFIG_GENERIC_LOCKBREAK, where sizeof(spinlock_t) == 8, but it easily fits into struct page. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Hugh Dickins <hughd@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-11-15lockref: use BLOATED_SPINLOCKS to avoid explicit config dependenciesPeter Zijlstra1-1/+6
Avoid the fragile Kconfig construct guestimating spinlock_t sizes; use a friendly compile-time test to determine this. [kirill.shutemov@linux.intel.com: drop CONFIG_CMPXCHG_LOCKREF] Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-10-15GFS2: Use lockref for glocksSteven Whitehouse1-0/+6
Currently glocks have an atomic reference count and also a spinlock which covers various internal fields, such as the state. This intent of this patch is to replace the spinlock and the atomic reference count with a lockref structure. This contains a spinlock which we can continue to use as before, and a reference counter which is used in conjuction with the spinlock to replace the previous atomic counter. As a result of this there are some new rules for reference counting on glocks. We need to distinguish between reference count changes under gl_spin (which are now just increment or decrement of the new counter, provided the count cannot hit zero) and those which are outside of gl_spin, but which now take gl_spin internally. The conversion is relatively straight forward. There is probably some further clean up which can be done, but the priority at this stage is to make the change in as simple a manner as possible. A consequence of this change is that the reference count is being decoupled from the lru list processing. This should allow future adoption of the lru_list code with glocks in due course. The reason for using the "dead" state and not just relying on 0 being the "invalid state" is so that in due course 0 ref counts can be allowable. The intent is to eventually be able to remove the ref count changes which are currently hidden away in state_change(). Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
2013-09-08lockref: add ability to mark lockrefs "dead"Linus Torvalds1-0/+3
The only actual current lockref user (dcache) uses zero reference counts even for perfectly live dentries, because it's a cache: there may not be any users, but that doesn't mean that we want to throw away the dentry. At the same time, the dentry cache does have a notion of a truly "dead" dentry that we must not even increment the reference count of, because we have pruned it and it is not valid. Currently that distinction is not visible in the lockref itself, and the dentry cache validation uses "lockref_get_or_lock()" to either get a new reference to a dentry that already had existing references (and thus cannot be dead), or get the dentry lock so that we can then verify the dentry and increment the reference count under the lock if that verification was successful. That's all somewhat complicated. This adds the concept of being "dead" to the lockref itself, by simply using a count that is negative. This allows a usage scenario where we can increment the refcount of a dentry without having to validate it, and pushing the special "we killed it" case into the lockref code. The dentry code itself doesn't actually use this yet, and it's probably too late in the merge window to do that code (the dentry_kill() code with its "should I decrement the count" logic really is pretty complex code), but let's introduce the concept at the lockref level now. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-09-02lockref: implement lockless reference count updates using cmpxchg()Linus Torvalds1-2/+9
Instead of taking the spinlock, the lockless versions atomically check that the lock is not taken, and do the reference count update using a cmpxchg() loop. This is semantically identical to doing the reference count update protected by the lock, but avoids the "wait for lock" contention that you get when accesses to the reference count are contended. Note that a "lockref" is absolutely _not_ equivalent to an atomic_t. Even when the lockref reference counts are updated atomically with cmpxchg, the fact that they also verify the state of the spinlock means that the lockless updates can never happen while somebody else holds the spinlock. So while "lockref_put_or_lock()" looks a lot like just another name for "atomic_dec_and_lock()", and both optimize to lockless updates, they are fundamentally different: the decrement done by atomic_dec_and_lock() is truly independent of any lock (as long as it doesn't decrement to zero), so a locked region can still see the count change. The lockref structure, in contrast, really is a *locked* reference count. If you hold the spinlock, the reference count will be stable and you can modify the reference count without using atomics, because even the lockless updates will see and respect the state of the lock. In order to enable the cmpxchg lockless code, the architecture needs to do three things: (1) Make sure that the "arch_spinlock_t" and an "unsigned int" can fit in an aligned u64, and have a "cmpxchg()" implementation that works on such a u64 data type. (2) define a helper function to test for a spinlock being unlocked ("arch_spin_value_unlocked()") (3) select the "ARCH_USE_CMPXCHG_LOCKREF" config variable in its Kconfig file. This enables it for x86-64 (but not 32-bit, we'd need to make sure cmpxchg() turns into the proper cmpxchg8b in order to enable it for 32-bit mode). Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-09-02lockref: uninline lockref helper functionsLinus Torvalds1-62/+4
They aren't very good to inline, since they already call external functions (the spinlock code), and we're going to create rather more complicated versions of them that can do the reference count updates locklessly. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-09-02lockref: add 'lockref_get_or_lock() helperLinus Torvalds1-0/+16
This behaves like "lockref_get_not_zero()", but instead of doing nothing if the count was zero, it returns with the lock held. This allows callers to revalidate the lockref-protected data structure if required even if the count was zero to begin with, and possibly increment the count if it passes muster. In particular, the dentry code wants this when it wants to turn an RCU-protected dentry into a stable refcounted one: if the dentry count it zero, but the sequence number still validates the dentry, we can take a reference to it. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-08-29Add new lockref infrastructure reference implementationWaiman Long1-0/+71
This introduces a new "lockref" structure that supports the concept of lockless updates of reference counts that still honor an attached spinlock. NOTE! This reference implementation is not the optimized lockless version, rather it is the fallback implementation using standard spinlocks. The actual optimized versions will be merged into 3.12, but I wanted to get the infrastructure in place and document the new interfaces. [ Also note that this particular commit is drastically cut-down minimal version of the original patch by Waiman. In order to properly credit the original author I'm marking Waiman as the author here, but in the end this patch bears little resemblance to the patch by Waiman. So blame any errors on me editing things down to the point where I can introduce the infrastructure before the merge window for 3.12 actually opens. - Linus ] Signed-off-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>