user/sven/linux.git/include/linux/backing-dev.h, branch v5.4.171

bdi: move bdi_dev_name out of line

2020-05-14T05:58:30Z

[ Upstream commit eb7ae5e06bb6e6ac6bb86872d27c43ebab92f6b2 ] bdi_dev_name is not a fast path function, move it out of line. This prepares for using it from modular callers without having to export an implementation detail like bdi_unknown_name. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Greg Kroah-Hartman Reviewed-by: Bart Van Assche Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin

memcg: fix a crash in wb_workfn when a device disappears

2020-02-11T12:35:11Z

commit 68f23b89067fdf187763e75a56087550624fdbee upstream. Without memcg, there is a one-to-one mapping between the bdi and bdi_writeback structures. In this world, things are fairly straightforward; the first thing bdi_unregister() does is to shutdown the bdi_writeback structure (or wb), and part of that writeback ensures that no other work queued against the wb, and that the wb is fully drained. With memcg, however, there is a one-to-many relationship between the bdi and bdi_writeback structures; that is, there are multiple wb objects which can all point to a single bdi. There is a refcount which prevents the bdi object from being released (and hence, unregistered). So in theory, the bdi_unregister() *should* only get called once its refcount goes to zero (bdi_put will drop the refcount, and when it is zero, release_bdi gets called, which calls bdi_unregister). Unfortunately, del_gendisk() in block/gen_hd.c never got the memo about the Brave New memcg World, and calls bdi_unregister directly. It does this without informing the file system, or the memcg code, or anything else. This causes the root wb associated with the bdi to be unregistered, but none of the memcg-specific wb's are shutdown. So when one of these wb's are woken up to do delayed work, they try to dereference their wb->bdi->dev to fetch the device name, but unfortunately bdi->dev is now NULL, thanks to the bdi_unregister() called by del_gendisk(). As a result, *boom*. Fortunately, it looks like the rest of the writeback path is perfectly happy with bdi->dev and bdi->owner being NULL, so the simplest fix is to create a bdi_dev_name() function which can handle bdi->dev being NULL. This also allows us to bulletproof the writeback tracepoints to prevent them from dereferencing a NULL pointer and crashing the kernel if one is tracing with memcg's enabled, and an iSCSI device dies or a USB storage stick is pulled. The most common way of triggering this will be hotremoval of a device while writeback with memcg enabled is going on. It was triggering several times a day in a heavily loaded production environment. Google Bug Id: 145475544 Link: https://lore.kernel.org/r/20191227194829.150110-1-tytso@mit.edu Link: http://lkml.kernel.org/r/20191228005211.163952-1-tytso@mit.edu Signed-off-by: Theodore Ts'o Cc: Chris Mason Cc: Tejun Heo Cc: Jens Axboe Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

writeback: Separate out wb_get_lookup() from wb_get_create()

2019-08-27T15:22:38Z

Separate out wb_get_lookup() which doesn't try to create one if there isn't already one from wb_get_create(). This will be used by later patches. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

bdi: Add bdi->id

2019-08-27T15:22:38Z

There currently is no way to universally identify and lookup a bdi without holding a reference and pointer to it. This patch adds an non-recycling bdi->id and implements bdi_get_by_id() which looks up bdis by their ids. This will be used by memcg foreign inode flushing. I left bdi_list alone for simplicity and because while rb_tree does support rcu assignment it doesn't seem to guarantee lossless walk when walk is racing aginst tree rebalance operations. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

writeback: Generalize and expose wb_completion

2019-08-27T15:22:38Z

wb_completion is used to track writeback completions. We want to use it from memcg side for foreign inode flushes. This patch updates it to remember the target waitq instead of assuming bdi->wb_waitq and expose it outside of fs-writeback.c. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

blkcg: implement REQ_CGROUP_PUNT

2019-07-10T15:00:57Z

When a shared kthread needs to issue a bio for a cgroup, doing so synchronously can lead to priority inversions as the kthread can be trapped waiting for that cgroup. This patch implements REQ_CGROUP_PUNT flag which makes submit_bio() punt the actual issuing to a dedicated per-blkcg work item to avoid such priority inversions. This will be used to fix priority inversions in btrfs compression and should be generally useful as we grow filesystem support for comprehensive IO control. Cc: Chris Mason Reviewed-by: Josef Bacik Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

writeback: fix inode cgroup switching comment

2019-03-06T05:07:21Z

Commit 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates") refers to inode_switch_wb_work_fn() which never got merged. Switch the comments to inode_switch_wbs_work_fn(). Link: http://lkml.kernel.org/r/20190305004617.142590-1-gthelen@google.com Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates") Signed-off-by: Greg Thelen Reviewed-by: Andrew Morton Acked-by: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

bdi: use refcount_t for reference counting instead atomic_t

2018-08-22T17:52:46Z

refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This permits avoiding accidental refcounter overflows that might lead to use-after-free situations. Link: http://lkml.kernel.org/r/20180703200141.28415-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Andrew Morton Acked-by: Peter Zijlstra (Intel) Suggested-by: Peter Zijlstra Cc: Jens Axboe Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

writeback: safer lock nesting

2018-04-21T00:18:35Z

lock_page_memcg()/unlock_page_memcg() use spin_lock_irqsave/restore() if the page's memcg is undergoing move accounting, which occurs when a process leaves its memcg for a new one that has memory.move_charge_at_immigrate set. unlocked_inode_to_wb_begin,end() use spin_lock_irq/spin_unlock_irq() if the given inode is switching writeback domains. Switches occur when enough writes are issued from a new domain. This existing pattern is thus suspicious: lock_page_memcg(page); unlocked_inode_to_wb_begin(inode, &locked); ... unlocked_inode_to_wb_end(inode, locked); unlock_page_memcg(page); If both inode switch and process memcg migration are both in-flight then unlocked_inode_to_wb_end() will unconditionally enable interrupts while still holding the lock_page_memcg() irq spinlock. This suggests the possibility of deadlock if an interrupt occurs before unlock_page_memcg(). truncate __cancel_dirty_page lock_page_memcg unlocked_inode_to_wb_begin unlocked_inode_to_wb_end end_page_writeback test_clear_page_writeback lock_page_memcg unlock_page_memcg Due to configuration limitations this deadlock is not currently possible because we don't mix cgroup writeback (a cgroupv2 feature) and memory.move_charge_at_immigrate (a cgroupv1 feature). If the kernel is hacked to always claim inode switching and memcg moving_account, then this script triggers lockup in less than a minute: cd /mnt/cgroup/memory mkdir a b echo 1 > a/memory.move_charge_at_immigrate echo 1 > b/memory.move_charge_at_immigrate ( echo $BASHPID > a/cgroup.procs while true; do dd if=/dev/zero of=/mnt/big bs=1M count=256 done ) & while true; do sync done & sleep 1h & SLEEP=$! while true; do echo $SLEEP > a/cgroup.procs echo $SLEEP > b/cgroup.procs done The deadlock does not seem possible, so it's debatable if there's any reason to modify the kernel. I suggest we should to prevent future surprises. And Wang Long said "this deadlock occurs three times in our environment", so there's more reason to apply this, even to stable. Stable 4.4 has minor conflicts applying this patch. For a clean 4.4 patch see "[PATCH for-4.4] writeback: safer lock nesting" https://lkml.org/lkml/2018/4/11/146 Wang Long said "this deadlock occurs three times in our environment" [gthelen@google.com: v4] Link: http://lkml.kernel.org/r/20180411084653.254724-1-gthelen@google.com [akpm@linux-foundation.org: comment tweaks, struct initialization simplification] Change-Id: Ibb773e8045852978f6207074491d262f1b3fb613 Link: http://lkml.kernel.org/r/20180410005908.167976-1-gthelen@google.com Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates") Signed-off-by: Greg Thelen Reported-by: Wang Long Acked-by: Wang Long Acked-by: Michal Hocko Reviewed-by: Andrew Morton Cc: Johannes Weiner Cc: Tejun Heo Cc: Nicholas Piggin Cc: [v4.2+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'for-linus-20180413' of git://git.kernel.dk/linux-block

2018-04-13T22:15:15Z

Pull block fixes from Jens Axboe: "Followup fixes for this merge window. This contains: - Series from Ming, fixing corner cases in our CPU <-> queue mapping. This triggered repeated warnings on especially s390, but I also hit it in cpu hot plug/unplug testing while doing IO on NVMe on x86-64. - Another fix from Ming, ensuring that we always order budget and driver tag identically, avoiding a deadlock on QD=1 devices. - Loop locking regression fix from this merge window, from Omar. - Another loop locking fix, this time missing an unlock, from Tetsuo Handa. - Fix for racing IO submission with device removal from Bart. - sr reference fix from me, fixing a case where disk change or getevents can race with device removal. - Set of nvme fixes by way of Keith, from various contributors" * tag 'for-linus-20180413' of git://git.kernel.dk/linux-block: (28 commits) nvme: expand nvmf_check_if_ready checks nvme: Use admin command effects for admin commands nvmet: fix space padding in serial number nvme: check return value of init_srcu_struct function nvmet: Fix nvmet_execute_write_zeroes sector count nvme-pci: Separate IO and admin queue IRQ vectors nvme-pci: Remove unused queue parameter nvme-pci: Skip queue deletion if there are no queues nvme: target: fix buffer overflow nvme: don't send keep-alives to the discovery controller nvme: unexport nvme_start_keep_alive nvme-loop: fix kernel oops in case of unhandled command nvme: enforce 64bit offset for nvme_get_log_ext fn sr: get/drop reference to device in revalidate and check_events blk-mq: Revert "blk-mq: reimplement blk_mq_hw_queue_mapped" blk-mq: Avoid that submitting a bio concurrently with device removal triggers a crash backing: silence compiler warning using __printf blk-mq: remove code for dealing with remapping queue blk-mq: reimplement blk_mq_hw_queue_mapped blk-mq: don't check queue mapped in __blk_mq_delay_run_hw_queue() ...