From: Andrew Morton <akpm@linux-foundation.org>
To: patrice.chotard@foss.st.com, mpatocka@redhat.com,
markhemm@googlemail.com, lczerner@redhat.com, hch@lst.de,
djwong@kernel.org, chuck.lever@oracle.com, hughd@google.com,
akpm@linux-foundation.org, patches@lists.linux.dev,
linux-mm@kvack.org, mm-commits@vger.kernel.org,
torvalds@linux-foundation.org, akpm@linux-foundation.org
Subject: [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE
Date: Thu, 14 Apr 2022 19:13:27 -0700 [thread overview]
Message-ID: <20220415021328.7D31EC385A1@smtp.kernel.org> (raw)
In-Reply-To: <20220414191240.9f86d15a3e3afd848a9839a6@linux-foundation.org>
From: Hugh Dickins <hughd@google.com>
Subject: tmpfs: fix regressions from wider use of ZERO_PAGE
Chuck Lever reported fsx-based xfstests generic 075 091 112 127 failing
when 5.18-rc1 NFS server exports tmpfs: bisected to recent tmpfs change.
Whilst nfsd_splice_action() does contain some questionable handling of
repeated pages, and Chuck was able to work around there, history from
Mark Hemment makes clear that there might be similar dangers elsewhere:
it was not a good idea for me to pass ZERO_PAGE down to unknown actors.
Revert shmem_file_read_iter() to using ZERO_PAGE for holes only when
iter_is_iovec(); in other cases, use the more natural iov_iter_zero()
instead of copy_page_to_iter(). We would use iov_iter_zero() throughout,
but the x86 clear_user() is not nearly so well optimized as copy to user
(dd of 1T sparse tmpfs file takes 57 seconds rather than 44 seconds).
And now pagecache_init() does not need to SetPageUptodate(ZERO_PAGE(0)):
which had caused boot failure on arm noMMU STM32F7 and STM32H7 boards
Link: https://lkml.kernel.org/r/9a978571-8648-e830-5735-1f4748ce2e30@google.com
Fixes: 56a8c8eb1eaf ("tmpfs: do not allocate pages on read")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Patrice CHOTARD <patrice.chotard@foss.st.com>
Reported-by: Chuck Lever III <chuck.lever@oracle.com>
Tested-by: Chuck Lever III <chuck.lever@oracle.com>
Cc: Mark Hemment <markhemm@googlemail.com>
Cc: Patrice CHOTARD <patrice.chotard@foss.st.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Lukas Czerner <lczerner@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/filemap.c | 6 ------
mm/shmem.c | 31 ++++++++++++++++++++-----------
2 files changed, 20 insertions(+), 17 deletions(-)
--- a/mm/filemap.c~tmpfs-fix-regressions-from-wider-use-of-zero_page
+++ a/mm/filemap.c
@@ -1063,12 +1063,6 @@ void __init pagecache_init(void)
init_waitqueue_head(&folio_wait_table[i]);
page_writeback_init();
-
- /*
- * tmpfs uses the ZERO_PAGE for reading holes: it is up-to-date,
- * and splice's page_cache_pipe_buf_confirm() needs to see that.
- */
- SetPageUptodate(ZERO_PAGE(0));
}
/*
--- a/mm/shmem.c~tmpfs-fix-regressions-from-wider-use-of-zero_page
+++ a/mm/shmem.c
@@ -2513,7 +2513,6 @@ static ssize_t shmem_file_read_iter(stru
pgoff_t end_index;
unsigned long nr, ret;
loff_t i_size = i_size_read(inode);
- bool got_page;
end_index = i_size >> PAGE_SHIFT;
if (index > end_index)
@@ -2570,24 +2569,34 @@ static ssize_t shmem_file_read_iter(stru
*/
if (!offset)
mark_page_accessed(page);
- got_page = true;
+ /*
+ * Ok, we have the page, and it's up-to-date, so
+ * now we can copy it to user space...
+ */
+ ret = copy_page_to_iter(page, offset, nr, to);
+ put_page(page);
+
+ } else if (iter_is_iovec(to)) {
+ /*
+ * Copy to user tends to be so well optimized, but
+ * clear_user() not so much, that it is noticeably
+ * faster to copy the zero page instead of clearing.
+ */
+ ret = copy_page_to_iter(ZERO_PAGE(0), offset, nr, to);
} else {
- page = ZERO_PAGE(0);
- got_page = false;
+ /*
+ * But submitting the same page twice in a row to
+ * splice() - or others? - can result in confusion:
+ * so don't attempt that optimization on pipes etc.
+ */
+ ret = iov_iter_zero(nr, to);
}
- /*
- * Ok, we have the page, and it's up-to-date, so
- * now we can copy it to user space...
- */
- ret = copy_page_to_iter(page, offset, nr, to);
retval += ret;
offset += ret;
index += offset >> PAGE_SHIFT;
offset &= ~PAGE_MASK;
- if (got_page)
- put_page(page);
if (!iov_iter_count(to))
break;
if (ret < nr) {
_
next prev parent reply other threads:[~2022-04-15 2:13 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-15 2:12 incoming Andrew Morton
2022-04-15 2:13 ` [patch 01/14] MAINTAINERS: Broadcom internal lists aren't maintainers Andrew Morton
2022-04-15 2:13 ` Andrew Morton [this message]
2022-04-15 22:10 ` [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE Linus Torvalds
2022-04-15 22:21 ` Matthew Wilcox
2022-04-15 22:41 ` Hugh Dickins
2022-04-16 6:36 ` Borislav Petkov
2022-04-16 14:07 ` Mark Hemment
2022-04-16 17:28 ` Borislav Petkov
2022-04-16 17:42 ` Linus Torvalds
2022-04-16 21:15 ` Borislav Petkov
2022-04-17 19:41 ` Borislav Petkov
2022-04-17 20:56 ` Linus Torvalds
2022-04-18 10:15 ` Borislav Petkov
2022-04-18 17:10 ` Linus Torvalds
2022-04-19 9:17 ` Borislav Petkov
2022-04-19 16:41 ` Linus Torvalds
2022-04-19 17:48 ` Borislav Petkov
2022-04-21 15:06 ` Borislav Petkov
2022-04-21 16:50 ` Linus Torvalds
2022-04-21 17:22 ` Linus Torvalds
2022-04-24 19:37 ` Borislav Petkov
2022-04-24 19:54 ` Linus Torvalds
2022-04-24 20:24 ` Linus Torvalds
2022-04-27 0:14 ` Borislav Petkov
2022-04-27 1:29 ` Linus Torvalds
2022-04-27 10:41 ` Borislav Petkov
2022-04-27 16:00 ` Linus Torvalds
2022-05-04 18:56 ` Borislav Petkov
2022-05-04 19:22 ` Linus Torvalds
2022-05-04 20:18 ` Borislav Petkov
2022-05-04 20:40 ` Linus Torvalds
2022-05-04 21:01 ` Borislav Petkov
2022-05-04 21:09 ` Linus Torvalds
2022-05-10 9:31 ` clear_user (was: [patch 02/14] tmpfs: fix regressions from wider use of ZERO_PAGE) Borislav Petkov
2022-05-10 17:17 ` Linus Torvalds
2022-05-10 17:28 ` Linus Torvalds
2022-05-10 18:10 ` Borislav Petkov
2022-05-10 18:57 ` Borislav Petkov
2022-05-24 12:32 ` [PATCH] x86/clear_user: Make it faster Borislav Petkov
2022-05-24 16:51 ` Linus Torvalds
2022-05-24 17:30 ` Borislav Petkov
2022-05-25 12:11 ` Mark Hemment
2022-05-27 11:28 ` Borislav Petkov
2022-05-27 11:10 ` Ingo Molnar
2022-06-22 14:21 ` Borislav Petkov
2022-06-22 15:06 ` Linus Torvalds
2022-06-22 20:14 ` Borislav Petkov
2022-06-22 21:07 ` Linus Torvalds
2022-06-23 9:41 ` Borislav Petkov
2022-07-05 17:01 ` [PATCH -final] " Borislav Petkov
2022-07-06 9:24 ` Alexey Dobriyan
2022-07-11 10:33 ` Borislav Petkov
2022-07-12 12:32 ` Alexey Dobriyan
2022-08-06 12:49 ` Borislav Petkov
2022-04-15 2:13 ` [patch 03/14] mm/secretmem: fix panic when growing a memfd_secret Andrew Morton
2022-04-15 2:13 ` [patch 04/14] irq_work: use kasan_record_aux_stack_noalloc() record callstack Andrew Morton
2022-04-15 2:13 ` [patch 05/14] kasan: fix hw tags enablement when KUNIT tests are disabled Andrew Morton
2022-04-15 2:13 ` [patch 06/14] mm, kfence: support kmem_dump_obj() for KFENCE objects Andrew Morton
2022-04-15 2:13 ` [patch 07/14] mm, page_alloc: fix build_zonerefs_node() Andrew Morton
2022-04-15 2:13 ` [patch 08/14] mm: fix unexpected zeroed page mapping with zram swap Andrew Morton
2022-04-15 2:13 ` [patch 09/14] mm: compaction: fix compiler warning when CONFIG_COMPACTION=n Andrew Morton
2022-04-15 2:13 ` [patch 10/14] hugetlb: do not demote poisoned hugetlb pages Andrew Morton
2022-04-15 2:13 ` [patch 11/14] revert "fs/binfmt_elf: fix PT_LOAD p_align values for loaders" Andrew Morton
2022-04-15 2:13 ` [patch 12/14] revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE" Andrew Morton
2022-04-15 2:14 ` [patch 13/14] mm/vmalloc: fix spinning drain_vmap_work after reading from /proc/vmcore Andrew Morton
2022-04-15 2:14 ` [patch 14/14] mm: kmemleak: take a full lowmem check in kmemleak_*_phys() Andrew Morton
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