linux.git/mm/page-writeback.c, branch v4.1

writeback: use |1 instead of +1 to protect against div by zero

2015-04-23T16:36:33+00:00

mm/page-writeback.c has several places where 1 is added to the divisor
to prevent division by zero exceptions; however, if the original
divisor is equivalent to -1, adding 1 leads to division by zero.

There are three places where +1 is used for this purpose - one in
pos_ratio_polynom() and two in bdi_position_ratio().  The second one
in bdi_position_ratio() actually triggered div-by-zero oops on a
machine running a 3.10 kernel.  The divisor is

  x_intercept - bdi_setpoint + 1 == span + 1

span is confirmed to be (u32)-1.  It isn't clear how it ended up that
but it could be from write bandwidth calculation underflow fixed by
c72efb658f7c ("writeback: fix possible underflow in write bandwidth
calculation").

At any rate, +1 isn't a proper protection against div-by-zero.  This
patch converts all +1 protections to |1.  Note that
bdi_update_dirty_ratelimit() was already using |1 before this patch.

Signed-off-by: Tejun Heo 
Cc: stable@vger.kernel.org
Reviewed-by: Jan Kara 
Signed-off-by: Jens Axboe

mm/page-writeback: check-before-clear PageReclaim

2015-04-15T23:35:17+00:00

With the page flag sanitization patchset, an invalid usage of
ClearPageReclaim() is detected in set_page_dirty().  This can be called
from __unmap_hugepage_range(), so let's check PageReclaim() before trying
to clear it to avoid the misuse.

Signed-off-by: Naoya Horiguchi 
Acked-by: Kirill A. Shutemov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

page_writeback: clean up mess around cancel_dirty_page()

2015-04-14T23:49:01+00:00

This patch replaces cancel_dirty_page() with a helper function
account_page_cleaned() which only updates counters.  It's called from
truncate_complete_page() and from try_to_free_buffers() (hack for ext3).
Page is locked in both cases, page-lock protects against concurrent
dirtiers: see commit 2d6d7f982846 ("mm: protect set_page_dirty() from
ongoing truncation").

Delete_from_page_cache() shouldn't be called for dirty pages, they must
be handled by caller (either written or truncated).  This patch treats
final dirty accounting fixup at the end of __delete_from_page_cache() as
a debug check and adds WARN_ON_ONCE() around it.  If something removes
dirty pages without proper handling that might be a bug and unwritten
data might be lost.

Hugetlbfs has no dirty pages accounting, ClearPageDirty() is enough
here.

cancel_dirty_page() in nfs_wb_page_cancel() is redundant.  This is
helper for nfs_invalidate_page() and it's called only in case complete
invalidation.

The mess was started in v2.6.20 after commits 46d2277c796f ("Clean up
and make try_to_free_buffers() not race with dirty pages") and
3e67c0987d75 ("truncate: clear page dirtiness before running
try_to_free_buffers()") first was reverted right in v2.6.20 in commit
ecdfc9787fe5 ("Resurrect 'try_to_free_buffers()' VM hackery"), second in
v2.6.25 commit a2b345642f53 ("Fix dirty page accounting leak with ext3
data=journal").

Custom fixes were introduced between these points.  NFS in v2.6.23, commit
1b3b4a1a2deb ("NFS: Fix a write request leak in nfs_invalidate_page()").
Kludge in __delete_from_page_cache() in v2.6.24, commit 3a6927906f1b ("Do
dirty page accounting when removing a page from the page cache").  Since
v2.6.25 all of them are redundant.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Konstantin Khlebnikov 
Cc: Tejun Heo 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

writeback: fix possible underflow in write bandwidth calculation

2015-03-23T15:35:58+00:00

From 1ebf33901ecc75d9496862dceb1ef0377980587c Mon Sep 17 00:00:00 2001
From: Tejun Heo 
Date: Mon, 23 Mar 2015 00:08:19 -0400

2f800fbd777b ("writeback: fix dirtied pages accounting on redirty")
introduced account_page_redirty() which reverts stat updates for a
redirtied page, making BDI_DIRTIED no longer monotonically increasing.

bdi_update_write_bandwidth() uses the delta in BDI_DIRTIED as the
basis for bandwidth calculation.  While unlikely, since the above
patch, the newer value may be lower than the recorded past value and
underflow the bandwidth calculation leading to a wild result.

Fix it by subtracing min of the old and new values when calculating
delta.  AFAIK, there hasn't been any report of it happening but the
resulting erratic behavior would be non-critical and temporary, so
it's possible that the issue is happening without being reported.  The
risk of the fix is very low, so tagged for -stable.

Signed-off-by: Tejun Heo 
Cc: Jens Axboe 
Cc: Jan Kara 
Cc: Wu Fengguang 
Cc: Greg Thelen 
Fixes: 2f800fbd777b ("writeback: fix dirtied pages accounting on redirty")
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe

writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()

2015-03-04T15:38:59+00:00

global_update_bandwidth() uses static variable update_time as the
timestamp for the last update but forgets to initialize it to
INITIALIZE_JIFFIES.

This means that global_dirty_limit will be 5 mins into the future on
32bit and some large amount jiffies into the past on 64bit.  This
isn't critical as the only effect is that global_dirty_limit won't be
updated for the first 5 mins after booting on 32bit machines,
especially given the auxiliary nature of global_dirty_limit's role -
protecting against global dirty threshold's sudden dips; however, it
does lead to unintended suboptimal behavior.  Fix it.

Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
Signed-off-by: Tejun Heo 
Acked-by: Jan Kara 
Cc: Wu Fengguang 
Cc: Jens Axboe 
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe

Merge branch 'for-3.20/bdi' of git://git.kernel.dk/linux-block

2015-02-12T21:50:21+00:00

Pull backing device changes from Jens Axboe:
 "This contains a cleanup of how the backing device is handled, in
  preparation for a rework of the life time rules.  In this part, the
  most important change is to split the unrelated nommu mmap flags from
  it, but also removing a backing_dev_info pointer from the
  address_space (and inode), and a cleanup of other various minor bits.

  Christoph did all the work here, I just fixed an oops with pages that
  have a swap backing.  Arnd fixed a missing export, and Oleg killed the
  lustre backing_dev_info from staging.  Last patch was from Al,
  unexporting parts that are now no longer needed outside"

* 'for-3.20/bdi' of git://git.kernel.dk/linux-block:
  Make super_blocks and sb_lock static
  mtd: export new mtd_mmap_capabilities
  fs: make inode_to_bdi() handle NULL inode
  staging/lustre/llite: get rid of backing_dev_info
  fs: remove default_backing_dev_info
  fs: don't reassign dirty inodes to default_backing_dev_info
  nfs: don't call bdi_unregister
  ceph: remove call to bdi_unregister
  fs: remove mapping->backing_dev_info
  fs: export inode_to_bdi and use it in favor of mapping->backing_dev_info
  nilfs2: set up s_bdi like the generic mount_bdev code
  block_dev: get bdev inode bdi directly from the block device
  block_dev: only write bdev inode on close
  fs: introduce f_op->mmap_capabilities for nommu mmap support
  fs: kill BDI_CAP_SWAP_BACKED
  fs: deduplicate noop_backing_dev_info

page_writeback: put account_page_redirty() after set_page_dirty()

2015-02-12T01:06:04+00:00

Helper account_page_redirty() fixes dirty pages counter for redirtied
pages.  This patch puts it after dirtying and prevents temporary
underflows of dirtied pages counters on zone/bdi and current->nr_dirtied.

Signed-off-by: Konstantin Khebnikov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: memcontrol: track move_lock state internally

2015-02-12T01:06:00+00:00

The complexity of memcg page stat synchronization is currently leaking
into the callsites, forcing them to keep track of the move_lock state and
the IRQ flags.  Simplify the API by tracking it in the memcg.

Signed-off-by: Johannes Weiner 
Acked-by: Michal Hocko 
Reviewed-by: Vladimir Davydov 
Cc: Wu Fengguang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: export inode_to_bdi and use it in favor of mapping->backing_dev_info

2015-01-20T21:03:04+00:00

Now that we got rid of the bdi abuse on character devices we can always use
sb->s_bdi to get at the backing_dev_info for a file, except for the block
device special case.  Export inode_to_bdi and replace uses of
mapping->backing_dev_info with it to prepare for the removal of
mapping->backing_dev_info.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Tejun Heo 
Reviewed-by: Jan Kara 
Signed-off-by: Jens Axboe

mm: protect set_page_dirty() from ongoing truncation

2015-01-08T23:10:51+00:00

Tejun, while reviewing the code, spotted the following race condition
between the dirtying and truncation of a page:

__set_page_dirty_nobuffers()       __delete_from_page_cache()
  if (TestSetPageDirty(page))
                                     page->mapping = NULL
				     if (PageDirty())
				       dec_zone_page_state(page, NR_FILE_DIRTY);
				       dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
    if (page->mapping)
      account_page_dirtied(page)
        __inc_zone_page_state(page, NR_FILE_DIRTY);
	__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);

which results in an imbalance of NR_FILE_DIRTY and BDI_RECLAIMABLE.

Dirtiers usually lock out truncation, either by holding the page lock
directly, or in case of zap_pte_range(), by pinning the mapcount with
the page table lock held.  The notable exception to this rule, though,
is do_wp_page(), for which this race exists.  However, do_wp_page()
already waits for a locked page to unlock before setting the dirty bit,
in order to prevent a race where clear_page_dirty() misses the page bit
in the presence of dirty ptes.  Upgrade that wait to a fully locked
set_page_dirty() to also cover the situation explained above.

Afterwards, the code in set_page_dirty() dealing with a truncation race
is no longer needed.  Remove it.

Reported-by: Tejun Heo 
Signed-off-by: Johannes Weiner 
Acked-by: Kirill A. Shutemov 
Reviewed-by: Jan Kara 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds