kernel/linux.git/mm/backing-dev.c, branch linux-4.16.y

bdi: Move cgroup bdi_writeback to a dedicated low concurrency workqueue

2018-06-25T23:54:01+00:00

commit f183464684190bacbfb14623bd3e4e51b7575b4c upstream. From 0aa2e9b921d6db71150633ff290199554f0842a8 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 23 May 2018 10:29:00 -0700 cgwb_release() punts the actual release to cgwb_release_workfn() on system_wq. Depending on the number of cgroups or block devices, there can be a lot of cgwb_release_workfn() in flight at the same time. We're periodically seeing close to 256 kworkers getting stuck with the following stack trace and overtime the entire system gets stuck. [] _synchronize_rcu_expedited.constprop.72+0x2fc/0x330 [] synchronize_rcu_expedited+0x24/0x30 [] bdi_unregister+0x53/0x290 [] release_bdi+0x89/0xc0 [] wb_exit+0x85/0xa0 [] cgwb_release_workfn+0x54/0xb0 [] process_one_work+0x150/0x410 [] worker_thread+0x6d/0x520 [] kthread+0x12c/0x160 [] ret_from_fork+0x29/0x40 [] 0xffffffffffffffff The events leading to the lockup are... 1. A lot of cgwb_release_workfn() is queued at the same time and all system_wq kworkers are assigned to execute them. 2. They all end up calling synchronize_rcu_expedited(). One of them wins and tries to perform the expedited synchronization. 3. However, that invovles queueing rcu_exp_work to system_wq and waiting for it. Because #1 is holding all available kworkers on system_wq, rcu_exp_work can't be executed. cgwb_release_workfn() is waiting for synchronize_rcu_expedited() which in turn is waiting for cgwb_release_workfn() to free up some of the kworkers. We shouldn't be scheduling hundreds of cgwb_release_workfn() at the same time. There's nothing to be gained from that. This patch updates cgwb release path to use a dedicated percpu workqueue with @max_active of 1. While this resolves the problem at hand, it might be a good idea to isolate rcu_exp_work to its own workqueue too as it can be used from various paths and is prone to this sort of indirect A-A deadlocks. Signed-off-by: Tejun Heo Cc: "Paul E. McKenney" Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bdi: Fix use after free bug in debugfs_remove()

2018-05-16T08:12:28+00:00

commit f53823c18131e755905b4f654196fd2cc3953f6e upstream. syzbot is reporting use after free bug in debugfs_remove() [1]. This is because fault injection made memory allocation for debugfs_create_file() from bdi_debug_register() from bdi_register_va() fail and continued with setting WB_registered. But when debugfs_remove() is called from debugfs_remove(bdi->debug_dir) from bdi_debug_unregister() from bdi_unregister() from release_bdi() because WB_registered was set by bdi_register_va(), IS_ERR_OR_NULL(bdi->debug_dir) == false despite debugfs_remove(bdi->debug_dir) was already called from bdi_register_va(). Fix this by making IS_ERR_OR_NULL(bdi->debug_dir) == true. [1] https://syzkaller.appspot.com/bug?id=5ab4efd91a96dcea9b68104f159adf4af2a6dfc1 Signed-off-by: Tetsuo Handa Reported-by: syzbot Fixes: 97f07697932e6faf ("bdi: convert bdi_debug_register to int") Cc: weiping zhang Reviewed-by: Greg Kroah-Hartman Reviewed-by: Jan Kara Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bdi: wake up concurrent wb_shutdown() callers.

2018-05-16T08:12:28+00:00

commit 8236b0ae31c837d2b3a2565c5f8d77f637e824cc upstream. syzbot is reporting hung tasks at wait_on_bit(WB_shutting_down) in wb_shutdown() [1]. This seems to be because commit 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") forgot to call wake_up_bit(WB_shutting_down) after clear_bit(WB_shutting_down). Introduce a helper function clear_and_wake_up_bit() and use it, in order to avoid similar errors in future. [1] https://syzkaller.appspot.com/bug?id=b297474817af98d5796bc544e1bb806fc3da0e5e Signed-off-by: Tetsuo Handa Reported-by: syzbot Fixes: 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") Cc: Tejun Heo Reviewed-by: Jan Kara Suggested-by: Linus Torvalds Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

Revert "bdi: add error handle for bdi_debug_register"

2017-12-21T17:01:30+00:00

This reverts commit a0747a859ef6d3cc5b6cd50eb694499b78dd0025. It breaks some booting for some users, and more than a week into this, there's still no good fix. Revert this commit for now until a solution has been found. Reported-by: Laura Abbott Reported-by: Bruno Wolff III Signed-off-by: Jens Axboe

bdi: add error handle for bdi_debug_register

2017-11-19T18:02:13+00:00

In order to make error handle more cleaner we call bdi_debug_register before set state to WB_registered, that we can avoid call bdi_unregister in release_bdi(). Reviewed-by: Jan Kara Signed-off-by: weiping zhang Signed-off-by: Jens Axboe

bdi: convert bdi_debug_register to int

2017-11-19T18:02:13+00:00

Convert bdi_debug_register to int and then do error handle for it. Reviewed-by: Jan Kara Signed-off-by: weiping zhang Signed-off-by: Jens Axboe

backing-dev: kill unused pdflush_proc_obsolete()

2017-10-06T14:15:15+00:00

After commit b35bd0d9f8a8, pdflush_proc_obsolete() is no longer used. Kill the function and declaration. Reported-by: Rakesh Pandit Signed-off-by: Jens Axboe

mm/backing-dev.c: fix an error handling path in 'cgwb_create()'

2017-09-11T20:16:44+00:00

If the 'kmalloc' fails, we must go through the existing error handling path. Signed-off-by: Christophe JAILLET Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") Reviewed-by: Jan Kara Signed-off-by: Jens Axboe

bdi: Drop 'parent' argument from bdi_register[_va]()

2017-04-20T18:09:55+00:00

Drop 'parent' argument of bdi_register() and bdi_register_va(). It is always NULL. Reviewed-by: Christoph Hellwig Signed-off-by: Jan Kara Signed-off-by: Jens Axboe

block: Remove unused functions

2017-04-20T18:09:55+00:00

Now that all backing_dev_info structure are allocated separately, we can drop some unused functions. Reviewed-by: Christoph Hellwig Signed-off-by: Jan Kara Signed-off-by: Jens Axboe