kernel.git/mm/fadvise.c, branch linux-4.18.y

mm/fadvise.c: fix signed overflow UBSAN complaint

2018-09-15T07:46:47Z

[ Upstream commit a718e28f538441a3b6612da9ff226973376cdf0f ] Signed integer overflow is undefined according to the C standard. The overflow in ksys_fadvise64_64() is deliberate, but since it is signed overflow, UBSAN complains: UBSAN: Undefined behaviour in mm/fadvise.c:76:10 signed integer overflow: 4 + 9223372036854775805 cannot be represented in type 'long long int' Use unsigned types to do math. Unsigned overflow is defined so UBSAN will not complain about it. This patch doesn't change generated code. [akpm@linux-foundation.org: add comment explaining the casts] Link: http://lkml.kernel.org/r/20180629184453.7614-1-aryabinin@virtuozzo.com Signed-off-by: Andrey Ryabinin Reported-by: Reviewed-by: Andrew Morton Cc: Alexander Potapenko Cc: Dmitry Vyukov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm: add ksys_fadvise64_64() helper; remove in-kernel call to sys_fadvise64_64()

2018-04-02T18:16:10Z

Using the ksys_fadvise64_64() helper allows us to avoid the in-kernel calls to the sys_fadvise64_64() syscall. The ksys_ prefix denotes that this function is meant as a drop-in replacement for the syscall. In particular, it uses the same calling convention as ksys_fadvise64_64(). Some compat stubs called sys_fadvise64(), which then just passed through the arguments to sys_fadvise64_64(). Get rid of this indirection, and call ksys_fadvise64_64() directly. This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Andrew Morton Cc: linux-mm@kvack.org Signed-off-by: Dominik Brodowski

mm/fadvise: discard partial page if endbyte is also EOF

2018-02-01T01:18:39Z

During our recent testing with fadvise(FADV_DONTNEED), we find that if given offset/length is not page-aligned, the last page will not be discarded. The tool we use is vmtouch (https://hoytech.com/vmtouch/), we map a 10KB-sized file into memory and then try to run this tool to evict the whole file mapping, but the last single page always remains staying in the memory: $./vmtouch -e test_10K Files: 1 Directories: 0 Evicted Pages: 3 (12K) Elapsed: 2.1e-05 seconds $./vmtouch test_10K Files: 1 Directories: 0 Resident Pages: 1/3 4K/12K 33.3% Elapsed: 5.5e-05 seconds However when we test with an older kernel, say 3.10, this problem is gone. So we wonder if this is a regression: $./vmtouch -e test_10K Files: 1 Directories: 0 Evicted Pages: 3 (12K) Elapsed: 8.2e-05 seconds $./vmtouch test_10K Files: 1 Directories: 0 Resident Pages: 0/3 0/12K 0% <-- partial page also discarded Elapsed: 5e-05 seconds After digging a little bit into this problem, we find it seems not a regression. Not discarding partial page is likely to be on purpose according to commit 441c228f817f ("mm: fadvise: document the fadvise(FADV_DONTNEED) behaviour for partial pages") written by Mel Gorman. He explained why partial pages should be preserved instead of being discarded when using fadvise(FADV_DONTNEED). However, the interesting part is that the actual code did NOT work as the same as it was described, the partial page was still discarded anyway, due to a calculation mistake of `end_index' passed to invalidate_mapping_pages(). This mistake has not been fixed until recently, that's why we fail to reproduce our problem in old kernels. The fix is done in commit 18aba41cbf ("mm/fadvise.c: do not discard partial pages with POSIX_FADV_DONTNEED") by Oleg Drokin. Back to the original testing, our problem becomes that there is a special case that, if the page-unaligned `endbyte' is also the end of file, it is not necessary at all to preserve the last partial page, as we all know no one else will use the rest of it. It should be safe enough if we just discard the whole page. So we add an EOF check in this patch. We also find a poosbile real world issue in mainline kernel. Assume such scenario: A userspace backup application want to backup a huge amount of small files (<4k) at once, the developer might (I guess) want to use fadvise(FADV_DONTNEED) to save memory. However, FADV_DONTNEED won't really happen since the only page mapped is a partial page, and kernel will preserve it. Our patch also fixes this problem, since we know the endbyte is EOF, so we discard it. Here is a simple reproducer to reproduce and verify each scenario we described above: test_fadvise.c ============================== #include #include #include #include #include #include #include int main(int argc, char **argv) { int i, fd, ret, len; struct stat buf; void *addr; unsigned char *vec; char *strbuf; ssize_t pagesize = getpagesize(); ssize_t filesize; fd = open(argv[1], O_RDWR|O_CREAT, S_IRUSR|S_IWUSR); if (fd < 0) return -1; filesize = strtoul(argv[2], NULL, 10); strbuf = malloc(filesize); memset(strbuf, 42, filesize); write(fd, strbuf, filesize); free(strbuf); fsync(fd); len = (filesize + pagesize - 1) / pagesize; printf("length of pages: %d\n", len); addr = mmap(NULL, filesize, PROT_READ, MAP_SHARED, fd, 0); if (addr == MAP_FAILED) return -1; ret = posix_fadvise(fd, 0, filesize, POSIX_FADV_DONTNEED); if (ret < 0) return -1; vec = malloc(len); ret = mincore(addr, filesize, (void *)vec); if (ret < 0) return -1; for (i = 0; i < len; i++) printf("pages[%d]: %x\n", i, vec[i] & 0x1); free(vec); close(fd); return 0; } ============================== Test 1: running on kernel with commit 18aba41cbf reverted: [root@caspar ~]# uname -r 4.15.0-rc6.revert+ [root@caspar ~]# ./test_fadvise file1 1024 length of pages: 1 pages[0]: 0 # <-- partial page discarded [root@caspar ~]# ./test_fadvise file2 8192 length of pages: 2 pages[0]: 0 pages[1]: 0 [root@caspar ~]# ./test_fadvise file3 10240 length of pages: 3 pages[0]: 0 pages[1]: 0 pages[2]: 0 # <-- partial page discarded Test 2: running on mainline kernel: [root@caspar ~]# uname -r 4.15.0-rc6+ [root@caspar ~]# ./test_fadvise test1 1024 length of pages: 1 pages[0]: 1 # <-- partial and the only page not discarded [root@caspar ~]# ./test_fadvise test2 8192 length of pages: 2 pages[0]: 0 pages[1]: 0 [root@caspar ~]# ./test_fadvise test3 10240 length of pages: 3 pages[0]: 0 pages[1]: 0 pages[2]: 1 # <-- partial page not discarded Test 3: running on kernel with this patch: [root@caspar ~]# uname -r 4.15.0-rc6.patched+ [root@caspar ~]# ./test_fadvise test1 1024 length of pages: 1 pages[0]: 0 # <-- partial page and EOF, discarded [root@caspar ~]# ./test_fadvise test2 8192 length of pages: 2 pages[0]: 0 pages[1]: 0 [root@caspar ~]# ./test_fadvise test3 10240 length of pages: 3 pages[0]: 0 pages[1]: 0 pages[2]: 0 # <-- partial page and EOF, discarded [akpm@linux-foundation.org: tweak code comment] Link: http://lkml.kernel.org/r/5222da9ee20e1695eaabb69f631f200d6e6b8876.1515132470.git.jinli.zjl@alibaba-inc.com Signed-off-by: shidao.ytt Signed-off-by: Caspar Zhang Reviewed-by: Oliver Yang Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

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

mm: fadvise: avoid fadvise for fs without backing device

2017-09-09T01:26:47Z

The fadvise() manpage is silent on fadvise()'s effect on memory-based filesystems (shmem, hugetlbfs & ramfs) and pseudo file systems (procfs, sysfs, kernfs). The current implementaion of fadvise is mostly a noop for such filesystems except for FADV_DONTNEED which will trigger expensive remote LRU cache draining. This patch makes the noop of fadvise() on such file systems very explicit. However this change has two side effects for ramfs and one for tmpfs. First fadvise(FADV_DONTNEED) could remove the unmapped clean zero'ed pages of ramfs (allocated through read, readahead & read fault) and tmpfs (allocated through read fault). Also fadvise(FADV_WILLNEED) could create such clean zero'ed pages for ramfs. This change removes those possibilities. One of our generic libraries does fadvise(FADV_DONTNEED). Recently we observed high latency in fadvise() and noticed that the users have started using tmpfs files and the latency was due to expensive remote LRU cache draining. For normal tmpfs files (have data written on them), fadvise(FADV_DONTNEED) will always trigger the unneeded remote cache draining. Link: http://lkml.kernel.org/r/20170818011023.181465-1-shakeelb@google.com Signed-off-by: Shakeel Butt Cc: Mel Gorman Cc: Johannes Weiner Cc: Hillf Danton Cc: Vlastimil Babka Cc: Hugh Dickins Cc: Greg Thelen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: fadvise: avoid expensive remote LRU cache draining after FADV_DONTNEED

2016-12-20T17:48:46Z

When FADV_DONTNEED cannot drop all pages in the range, it observes that some pages might still be on per-cpu LRU caches after recent instantiation and so initiates remote calls to all CPUs to flush their local caches. However, in most cases, the fadvise happens from the same context that instantiated the pages, and any pre-LRU pages in the specified range are most likely sitting on the local CPU's LRU cache, and so in many cases this results in unnecessary remote calls, which, in a loaded system, can hold up the fadvise() call significantly. [ I didn't record it in the extreme case we observed at Facebook, unfortunately. We had a slow-to-respond system and noticed it lru_add_drain_all() leading the profile during fadvise calls. This patch came out of thinking about the code and how we commonly call FADV_DONTNEED. FWIW, I wrote a silly directory tree walker/searcher that recurses through /usr to read and FADV_DONTNEED each file it finds. On a 2 socket 40 ht machine, over 1% is spent in lru_add_drain_all(). With the patch, that cost is gone; the local drain cost shows at 0.09%. ] Try to avoid the remote call by flushing the local LRU cache before even attempting to invalidate anything. It's a cheap operation, and the local LRU cache is the most likely to hold any pre-LRU pages in the specified fadvise range. Link: http://lkml.kernel.org/r/20161214210017.GA1465@cmpxchg.org Signed-off-by: Johannes Weiner Acked-by: Vlastimil Babka Acked-by: Mel Gorman Acked-by: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/fadvise.c: do not discard partial pages with POSIX_FADV_DONTNEED

2016-06-09T21:23:11Z

I noticed that the logic in the fadvise64_64 syscall is incorrect for partial pages. While first page of the region is correctly skipped if it is partial, the last page of the region is mistakenly discarded. This leads to problems for applications that read data in non-page-aligned chunks discarding already processed data between the reads. A somewhat misguided application that does something like write(XX bytes (non-page-alligned)); drop the data it just wrote; repeat gets a significant penalty in performance as a result. Link: http://lkml.kernel.org/r/1464917140-1506698-1-git-send-email-green@linuxhacker.ru Signed-off-by: Oleg Drokin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros

2016-04-04T17:41:08Z

PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time ago with promise that one day it will be possible to implement page cache with bigger chunks than PAGE_SIZE. This promise never materialized. And unlikely will. We have many places where PAGE_CACHE_SIZE assumed to be equal to PAGE_SIZE. And it's constant source of confusion on whether PAGE_CACHE_* or PAGE_* constant should be used in a particular case, especially on the border between fs and mm. Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much breakage to be doable. Let's stop pretending that pages in page cache are special. They are not. The changes are pretty straight-forward: - << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> ; - >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> ; - PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN}; - page_cache_get() -> get_page(); - page_cache_release() -> put_page(); This patch contains automated changes generated with coccinelle using script below. For some reason, coccinelle doesn't patch header files. I've called spatch for them manually. The only adjustment after coccinelle is revert of changes to PAGE_CAHCE_ALIGN definition: we are going to drop it later. There are few places in the code where coccinelle didn't reach. I'll fix them manually in a separate patch. Comments and documentation also will be addressed with the separate patch. virtual patch @@ expression E; @@ - E << (PAGE_CACHE_SHIFT - PAGE_SHIFT) + E @@ expression E; @@ - E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) + E @@ @@ - PAGE_CACHE_SHIFT + PAGE_SHIFT @@ @@ - PAGE_CACHE_SIZE + PAGE_SIZE @@ @@ - PAGE_CACHE_MASK + PAGE_MASK @@ expression E; @@ - PAGE_CACHE_ALIGN(E) + PAGE_ALIGN(E) @@ expression E; @@ - page_cache_get(E) + get_page(E) @@ expression E; @@ - page_cache_release(E) + put_page(E) Signed-off-by: Kirill A. Shutemov Acked-by: Michal Hocko Signed-off-by: Linus Torvalds

writeback: implement and use inode_congested()

2015-06-02T14:33:35Z

In several places, bdi_congested() and its wrappers are used to determine whether more IOs should be issued. With cgroup writeback support, this question can't be answered solely based on the bdi (backing_dev_info). It's dependent on whether the filesystem and bdi support cgroup writeback and the blkcg the inode is associated with. This patch implements inode_congested() and its wrappers which take @inode and determines the congestion state considering cgroup writeback. The new functions replace bdi_*congested() calls in places where the query is about specific inode and task. There are several filesystem users which also fit this criteria but they should be updated when each filesystem implements cgroup writeback support. v2: Now that a given inode is associated with only one wb, congestion state can be determined independent from the asking task. Drop @task. Spotted by Vivek. Also, converted to take @inode instead of @mapping and renamed to inode_congested(). Signed-off-by: Tejun Heo Cc: Jens Axboe Cc: Jan Kara Cc: Vivek Goyal Signed-off-by: Jens Axboe

vfs: remove get_xip_mem

2015-02-17T01:56:03Z

All callers of get_xip_mem() are now gone. Remove checks for it, initialisers of it, documentation of it and the only implementation of it. Also remove mm/filemap_xip.c as it is now empty. Also remove documentation of the long-gone get_xip_page(). Signed-off-by: Matthew Wilcox Cc: Andreas Dilger Cc: Boaz Harrosh Cc: Christoph Hellwig Cc: Dave Chinner Cc: Jan Kara Cc: Jens Axboe Cc: Kirill A. Shutemov Cc: Mathieu Desnoyers Cc: Randy Dunlap Cc: Ross Zwisler Cc: Theodore Ts'o Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds