kernel/linux.git/include/linux/backing-dev.h, branch linux-4.3.y

block: don't release bdi while request_queue has live references

2015-10-15T15:53:28+00:00

bdi's are initialized in two steps, bdi_init() and bdi_register(), but destroyed in a single step by bdi_destroy() which, for a bdi embedded in a request_queue, is called during blk_cleanup_queue() which makes the queue invisible and starts the draining of remaining usages. A request_queue's user can access the congestion state of the embedded bdi as long as it holds a reference to the queue. As such, it may access the congested state of a queue which finished blk_cleanup_queue() but hasn't reached blk_release_queue() yet. Because the congested state was embedded in backing_dev_info which in turn is embedded in request_queue, accessing the congested state after bdi_destroy() was called was fine. The bdi was destroyed but the memory region for the congested state remained accessible till the queue got released. a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") changed the situation. Now, the root congested state which is expected to be pinned while request_queue remains accessible is separately reference counted and the base ref is put during bdi_destroy(). This means that the root congested state may go away prematurely while the queue is between bdi_dstroy() and blk_cleanup_queue(), which was detected by Andrey's KASAN tests. The root cause of this problem is that bdi doesn't distinguish the two steps of destruction, unregistration and release, and now the root congested state actually requires a separate release step. To fix the issue, this patch separates out bdi_unregister() and bdi_exit() from bdi_destroy(). bdi_unregister() is called from blk_cleanup_queue() and bdi_exit() from blk_release_queue(). bdi_destroy() is now just a simple wrapper calling the two steps back-to-back. While at it, the prototype of bdi_destroy() is moved right below bdi_setup_and_register() so that the counterpart operations are located together. Signed-off-by: Tejun Heo Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") Cc: stable@vger.kernel.org # v4.2+ Reported-and-tested-by: Andrey Konovalov Link: http://lkml.kernel.org/g/CAAeHK+zUJ74Zn17=rOyxacHU18SgCfC6bsYW=6kCY5GXJBwGfQ@mail.gmail.com Reviewed-by: Jan Kara Reviewed-by: Jeff Moyer Signed-off-by: Jens Axboe

writeback: bdi_writeback iteration must not skip dying ones

2015-10-12T16:31:12+00:00

bdi_for_each_wb() is used in several places to wake up or issue writeback work items to all wb's (bdi_writeback's) on a given bdi. The iteration is performed by walking bdi->cgwb_tree; however, the tree only indexes wb's which are currently active. For example, when a memcg gets associated with a different blkcg, the old wb is removed from the tree so that the new one can be indexed. The old wb starts dying from then on but will linger till all its inodes are drained. As these dying wb's may still host dirty inodes, writeback operations which affect all wb's must include them. bdi_for_each_wb() skipping dying wb's led to sync(2) missing and failing to sync the inodes belonging to those wb's. This patch adds a RCU protected @bdi->wb_list which lists all wb's beloinging to that bdi. wb's are added on creation and removed on release rather than on the start of destruction. bdi_for_each_wb() usages are replaced with list_for_each[_continue]_rcu() iterations over @bdi->wb_list and bdi_for_each_wb() and its helpers are removed. v2: Updated as per Jan. last_wb ref leak in bdi_split_work_to_wbs() fixed and unnecessary list head severing in cgwb_bdi_destroy() removed. Signed-off-by: Tejun Heo Reported-and-tested-by: Artem Bityutskiy Fixes: ebe41ab0c79d ("writeback: implement bdi_for_each_wb()") Link: http://lkml.kernel.org/g/1443012552.19983.209.camel@gmail.com Cc: Jan Kara Signed-off-by: Jens Axboe

cgroup, writeback: don't enable cgroup writeback on traditional hierarchies

2015-09-24T20:48:52+00:00

inode_cgwb_enabled() gates cgroup writeback support. If it returns true, each inode is attached to the corresponding memory domain which gets mapped to io domain. It currently only tests whether the filesystem and bdi support cgroup writeback; however, cgroup writeback support doesn't work on traditional hierarchies and thus it should also test whether memcg and iocg are on the default hierarchy. This caused traditional hierarchy setups to hit the cgroup writeback path inadvertently and ended up creating separate writeback domains for each memcg and mapping them all to the root iocg uncovering a couple issues in the cgroup writeback path. cgroup writeback was never meant to be enabled on traditional hierarchies. Make inode_cgwb_enabled() test whether both memcg and iocg are on the default hierarchy. Signed-off-by: Tejun Heo Reported-by: Artem Bityutskiy Reported-by: Dexuan Cui Link: http://lkml.kernel.org/g/1443012552.19983.209.camel@gmail.com Link: http://lkml.kernel.org/g/f30d4a6aa8a546ff88f73021d026a453@SIXPR30MB031.064d.mgd.msft.net

blkcg: rename subsystem name from blkio to io

2015-08-18T22:49:18+00:00

blkio interface has become messy over time and is currently the largest. In addition to the inconsistent naming scheme, it has multiple stat files which report more or less the same thing, a number of debug stat files which expose internal details which shouldn't have been part of the public interface in the first place, recursive and non-recursive stats and leaf and non-leaf knobs. Both recursive vs. non-recursive and leaf vs. non-leaf distinctions don't make any sense on the unified hierarchy as only leaf cgroups can contain processes. cgroups is going through a major interface revision with the unified hierarchy involving significant fundamental usage changes and given that a significant portion of the interface doesn't make sense anymore, it's a good time to reorganize the interface. As the first step, this patch renames the external visible subsystem name from "blkio" to "io". This is more concise, matches the other two major subsystem names, "cpu" and "memory", and better suited as blkcg will be involved in anything writeback related too whether an actual block device is involved or not. As the subsystem legacy_name is set to "blkio", the only userland visible change outside the unified hierarchy is that blkcg is reported as "io" instead of "blkio" in the subsystem initialized message during boot. On the unified hierarchy, blkcg now appears as "io". Signed-off-by: Tejun Heo Cc: Li Zefan Cc: Johannes Weiner Cc: cgroups@vger.kernel.org Signed-off-by: Jens Axboe

writeback: bdi_for_each_wb() iteration is memcg ID based not blkcg

2015-08-18T22:49:15+00:00

wb's (bdi_writeback's) are currently keyed by memcg ID; however, in an earlier implementation, wb's were keyed by blkcg ID. bdi_for_each_wb() walks bdi->cgwb_tree in the ascending ID order and allows iterations to start from an arbitrary ID which is used to interrupt and resume iterations. Unfortunately, while changing wb to be keyed by memcg ID instead of blkcg, bdi_for_each_wb() was missed and is still assuming that wb's are keyed by blkcg ID. This doesn't affect iterations which don't get interrupted but bdi_split_work_to_wbs() makes use of iteration resuming on allocation failures and thus may incorrectly skip or repeat wb's. Fix it by changing bdi_for_each_wb() to take memcg IDs instead of blkcg IDs and updating bdi_split_work_to_wbs() accordingly. Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

writeback: don't embed root bdi_writeback_congested in bdi_writeback

2015-07-02T14:46:00+00:00

52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") made bdi (backing_dev_info) host per-cgroup wb's (bdi_writeback's). As the congested state needs to be per-wb and referenced from blkcg side and multiple wbs, the patch made all non-root cong's (bdi_writeback_congested's) reference counted and indexed on bdi. When a bdi is destroyed, cgwb_bdi_destroy() tries to drain all non-root cong's; however, this can hang indefinitely because wb's can also be referenced from blkcg_gq's which are destroyed after bdi destruction is complete. To fix the bug, bdi destruction will be updated to not wait for cong's to drain, which naturally means that cong's may outlive the associated bdi. This is fine for non-root cong's but is problematic for the root cong's which are embedded in their bdi's as they may end up getting dereferenced after the containing bdi's are freed. This patch makes root cong's behave the same as non-root cong's. They are no longer embedded in their bdi's but allocated separately during bdi initialization, indexed and reference counted the same way. * As cong handling is the same for all wb's, wb->congested initialization is moved into wb_init(). * When !CONFIG_CGROUP_WRITEBACK, there was no indexing or refcnting. bdi->wb_congested is now a pointer pointing to the root cong allocated during bdi init and minimal refcnting operations are implemented. * The above makes root wb init paths diverge depending on CONFIG_CGROUP_WRITEBACK. root wb init is moved to cgwb_bdi_init(). This patch in itself shouldn't cause any consequential behavior differences but prepares for the actual fix. Signed-off-by: Tejun Heo Reported-by: Jon Christopherson Link: https://bugzilla.kernel.org/show_bug.cgi?id=100681 Tested-by: Jon Christopherson Added include to backing-dev.h for kfree() definition. Signed-off-by: Jens Axboe

Merge branch 'for-4.2/writeback' of git://git.kernel.dk/linux-block

2015-06-25T23:00:17+00:00

Pull cgroup writeback support from Jens Axboe: "This is the big pull request for adding cgroup writeback support. This code has been in development for a long time, and it has been simmering in for-next for a good chunk of this cycle too. This is one of those problems that has been talked about for at least half a decade, finally there's a solution and code to go with it. Also see last weeks writeup on LWN: http://lwn.net/Articles/648292/" * 'for-4.2/writeback' of git://git.kernel.dk/linux-block: (85 commits) writeback, blkio: add documentation for cgroup writeback support vfs, writeback: replace FS_CGROUP_WRITEBACK with SB_I_CGROUPWB writeback: do foreign inode detection iff cgroup writeback is enabled v9fs: fix error handling in v9fs_session_init() bdi: fix wrong error return value in cgwb_create() buffer: remove unusued 'ret' variable writeback: disassociate inodes from dying bdi_writebacks writeback: implement foreign cgroup inode bdi_writeback switching writeback: add lockdep annotation to inode_to_wb() writeback: use unlocked_inode_to_wb transaction in inode_congested() writeback: implement unlocked_inode_to_wb transaction and use it for stat updates writeback: implement [locked_]inode_to_wb_and_lock_list() writeback: implement foreign cgroup inode detection writeback: make writeback_control track the inode being written back writeback: relocate wb[_try]_get(), wb_put(), inode_{attach|detach}_wb() mm: vmscan: disable memcg direct reclaim stalling if cgroup writeback support is in use writeback: implement memcg writeback domain based throttling writeback: reset wb_domain->dirty_limit[_tstmp] when memcg domain size changes writeback: implement memcg wb_domain writeback: update wb_over_bg_thresh() to use wb_domain aware operations ...

vfs, writeback: replace FS_CGROUP_WRITEBACK with SB_I_CGROUPWB

2015-06-17T18:47:39+00:00

FS_CGROUP_WRITEBACK indicates whether a file_system_type supports cgroup writeback; however, different super_blocks of the same file_system_type may or may not support cgroup writeback depending on filesystem options. This patch replaces FS_CGROUP_WRITEBACK with a per-super_block flag. super_block->s_flags carries some internal flags in the high bits but it's exposd to userland through uapi header and running out of space anyway. This patch adds a new field super_block->s_iflags to carry kernel-internal flags. It is currently only used by the new SB_I_CGROUPWB flag whose concatenated and abbreviated name is for consistency with other super_block flags. ext2_fill_super() is updated to set SB_I_CGROUPWB. v2: Added super_block->s_iflags instead of stealing another high bit from sb->s_flags as suggested by Christoph and Jan. Signed-off-by: Tejun Heo Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Cc: Christoph Hellwig Cc: Jan Kara Cc: linux-ext4@vger.kernel.org Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe

writeback: add lockdep annotation to inode_to_wb()

2015-06-02T14:40:20+00:00

With the previous three patches, all operations which acquire wb from inode are either under one of inode->i_lock, mapping->tree_lock or wb->list_lock or protected by unlocked_inode_to_wb transaction. This will be depended upon by foreign inode wb switching. This patch adds lockdep assertion to inode_to_wb() so that usages outside the above list locks can be caught easily. There are three exceptions. * locked_inode_to_wb_and_lock_list() is holding wb->list_lock but the wb may not be the inode's. Ensuring that is the function's role after all. Updated to deref inode->i_wb directly. * inode_wb_stat_unlocked_begin() is usually protected by combination of !I_WB_SWITCH and rcu_read_lock(). Updated to deref inode->i_wb directly. * inode_congested() wants to test whether inode->i_wb is set before starting the transaction. Added inode_to_wb_is_valid() which tests inode->i_wb directly. v5: might_lock() removed. It annotates that the lock is grabbed w/ irq enabled which isn't the case and triggering lockdep warning spuriously. v4: might_lock() added to unlocked_inode_to_wb_begin(). v3: inode_congested() conversion added. v2: locked_inode_to_wb_and_lock_list() was missing in the first version. Signed-off-by: Tejun Heo Cc: Jens Axboe Cc: Jan Kara Cc: Wu Fengguang Cc: Greg Thelen Signed-off-by: Jens Axboe

writeback: implement unlocked_inode_to_wb transaction and use it for stat updates

2015-06-02T14:40:20+00:00

The mechanism for detecting whether an inode should switch its wb (bdi_writeback) association is now in place. This patch build the framework for the actual switching. This patch adds a new inode flag I_WB_SWITCHING, which has two functions. First, the easy one, it ensures that there's only one switching in progress for a give inode. Second, it's used as a mechanism to synchronize wb stat updates. The two stats, WB_RECLAIMABLE and WB_WRITEBACK, aren't event counters but track the current number of dirty pages and pages under writeback respectively. As such, when an inode is moved from one wb to another, the inode's portion of those stats have to be transferred together; unfortunately, this is a bit tricky as those stat updates are percpu operations which are performed without holding any lock in some places. This patch solves the problem in a similar way as memcg. Each such lockless stat updates are wrapped in transaction surrounded by unlocked_inode_to_wb_begin/end(). During normal operation, they map to rcu_read_lock/unlock(); however, if I_WB_SWITCHING is asserted, mapping->tree_lock is grabbed across the transaction. In turn, the switching path sets I_WB_SWITCHING and waits for a RCU grace period to pass before actually starting to switch, which guarantees that all stat update paths are synchronizing against mapping->tree_lock. This patch still doesn't implement the actual switching. v3: Updated on top of the recent cancel_dirty_page() updates. unlocked_inode_to_wb_begin() now nests inside mem_cgroup_begin_page_stat() to match the locking order. v2: The i_wb access transaction will be used for !stat accesses too. Function names and comments updated accordingly. s/inode_wb_stat_unlocked_{begin|end}/unlocked_inode_to_wb_{begin|end}/ s/switch_wb/switch_wbs/ Signed-off-by: Tejun Heo Cc: Jens Axboe Cc: Jan Kara Cc: Wu Fengguang Cc: Greg Thelen Signed-off-by: Jens Axboe