kernel_optimize_test/include
Nick Piggin d00806b183 mm: fix fault vs invalidate race for linear mappings
Fix the race between invalidate_inode_pages and do_no_page.

Andrea Arcangeli identified a subtle race between invalidation of pages from
pagecache with userspace mappings, and do_no_page.

The issue is that invalidation has to shoot down all mappings to the page,
before it can be discarded from the pagecache.  Between shooting down ptes to
a particular page, and actually dropping the struct page from the pagecache,
do_no_page from any process might fault on that page and establish a new
mapping to the page just before it gets discarded from the pagecache.

The most common case where such invalidation is used is in file truncation.
This case was catered for by doing a sort of open-coded seqlock between the
file's i_size, and its truncate_count.

Truncation will decrease i_size, then increment truncate_count before
unmapping userspace pages; do_no_page will read truncate_count, then find the
page if it is within i_size, and then check truncate_count under the page
table lock and back out and retry if it had subsequently been changed (ptl
will serialise against unmapping, and ensure a potentially updated
truncate_count is actually visible).

Complexity and documentation issues aside, the locking protocol fails in the
case where we would like to invalidate pagecache inside i_size.  do_no_page
can come in anytime and filemap_nopage is not aware of the invalidation in
progress (as it is when it is outside i_size).  The end result is that
dangling (->mapping == NULL) pages that appear to be from a particular file
may be mapped into userspace with nonsense data.  Valid mappings to the same
place will see a different page.

Andrea implemented two working fixes, one using a real seqlock, another using
a page->flags bit.  He also proposed using the page lock in do_no_page, but
that was initially considered too heavyweight.  However, it is not a global or
per-file lock, and the page cacheline is modified in do_no_page to increment
_count and _mapcount anyway, so a further modification should not be a large
performance hit.  Scalability is not an issue.

This patch implements this latter approach.  ->nopage implementations return
with the page locked if it is possible for their underlying file to be
invalidated (in that case, they must set a special vm_flags bit to indicate
so).  do_no_page only unlocks the page after setting up the mapping
completely.  invalidation is excluded because it holds the page lock during
invalidation of each page (and ensures that the page is not mapped while
holding the lock).

This also allows significant simplifications in do_no_page, because we have
the page locked in the right place in the pagecache from the start.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-19 10:04:41 -07:00
..
acpi
asm-alpha alpha termios.h hadn't been updated 2007-07-17 11:01:07 -07:00
asm-arm
asm-arm26
asm-avr32 [AVR32] Fix atomic_add_unless() and atomic_sub_unless() 2007-07-18 20:47:04 +02:00
asm-blackfin
asm-cris
asm-frv
asm-generic saner typechecking in generic unaligned.h 2007-07-17 11:01:07 -07:00
asm-h8300
asm-i386 Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4 2007-07-18 10:32:00 -07:00
asm-ia64 Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux-2.6 2007-07-17 11:31:57 -07:00
asm-m32r
asm-m68k
asm-m68knommu
asm-mips zs: move to the serial subsystem 2007-07-18 08:38:22 -07:00
asm-parisc
asm-powerpc sys_fallocate() implementation on i386, x86_64 and powerpc 2007-07-17 21:42:44 -04:00
asm-ppc
asm-s390
asm-sh
asm-sh64
asm-sparc
asm-sparc64 [SPARC]: Mark sparc and sparc64 as not having virt_to_bus 2007-07-18 01:20:22 -07:00
asm-um
asm-v850
asm-x86_64 sys_fallocate() implementation on i386, x86_64 and powerpc 2007-07-17 21:42:44 -04:00
asm-xtensa
crypto
keys
linux mm: fix fault vs invalidate race for linear mappings 2007-07-19 10:04:41 -07:00
math-emu
media V4L/DVB (5835): saa7146/dvb-ttpci: Fix signedness warnings (gcc 4.1.1, kernel 2.6.22) 2007-07-18 14:24:44 -03:00
mtd UBI: kill homegrown endian macros 2007-07-18 16:53:49 +03:00
net [XFRM]: Fix crash introduced by struct dst_entry reordering 2007-07-18 01:55:52 -07:00
pcmcia
rdma
rxrpc
scsi
sound
video tgafb: actually allocate memory for the pseudo_palette 2007-07-17 10:23:12 -07:00
xen xen: Place vcpu_info structure into per-cpu memory 2007-07-18 08:47:45 -07:00
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