kernel/linux.git/lib/percpu_counter.c, branch v6.6.132

pcpcntr: add group allocation/free

2023-08-25T15:06:53+00:00

Allocations and frees are globally serialized on the pcpu lock (and the CPU hotplug lock if enabled, which is the case on Debian). At least one frequent consumer allocates 4 back-to-back counters (and frees them in the same manner), exacerbating the problem. While this does not fully remedy scalability issues, it is a step towards that goal and provides immediate relief. Signed-off-by: Mateusz Guzik Reviewed-by: Dennis Zhou Reviewed-by: Vegard Nossum Link: https://lore.kernel.org/r/20230823050609.2228718-2-mjguzik@gmail.com [Dennis: reflowed a few lines] Signed-off-by: Dennis Zhou

pcpcntr: remove percpu_counter_sum_all()

2023-03-19T17:02:04+00:00

percpu_counter_sum_all() is now redundant as the race condition it was invented to handle is now dealt with by percpu_counter_sum() directly and all users of percpu_counter_sum_all() have been removed. Remove it. This effectively reverts the changes made in f689054aace2 ("percpu_counter: add percpu_counter_sum_all interface") except for the cpumask iteration that fixes percpu_counter_sum() made earlier in this series. Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong

pcpcntrs: fix dying cpu summation race

2023-03-19T17:02:04+00:00

In commit f689054aace2 ("percpu_counter: add percpu_counter_sum_all interface") a race condition between a cpu dying and percpu_counter_sum() iterating online CPUs was identified. The solution was to iterate all possible CPUs for summation via percpu_counter_sum_all(). We recently had a percpu_counter_sum() call in XFS trip over this same race condition and it fired a debug assert because the filesystem was unmounting and the counter *should* be zero just before we destroy it. That was reported here: https://lore.kernel.org/linux-kernel/20230314090649.326642-1-yebin@huaweicloud.com/ likely as a result of running generic/648 which exercises filesystems in the presence of CPU online/offline events. The solution to use percpu_counter_sum_all() is an awful one. We use percpu counters and percpu_counter_sum() for accurate and reliable threshold detection for space management, so a summation race condition during these operations can result in overcommit of available space and that may result in filesystem shutdowns. As percpu_counter_sum_all() iterates all possible CPUs rather than just those online or even those present, the mask can include CPUs that aren't even installed in the machine, or in the case of machines that can hot-plug CPU capable nodes, even have physical sockets present in the machine. Fundamentally, this race condition is caused by the CPU being offlined being removed from the cpu_online_mask before the notifier that cleans up per-cpu state is run. Hence percpu_counter_sum() will not sum the count for a cpu currently being taken offline, regardless of whether the notifier has run or not. This is the root cause of the bug. The percpu counter notifier iterates all the registered counters, locks the counter and moves the percpu count to the global sum. This is serialised against other operations that move the percpu counter to the global sum as well as percpu_counter_sum() operations that sum the percpu counts while holding the counter lock. Hence the notifier is safe to run concurrently with sum operations, and the only thing we actually need to care about is that percpu_counter_sum() iterates dying CPUs. That's trivial to do, and when there are no CPUs dying, it has no addition overhead except for a cpumask_or() operation. This change makes percpu_counter_sum() always do the right thing in the presence of CPU hot unplug events and makes percpu_counter_sum_all() unnecessary. This, in turn, means that filesystems like XFS, ext4, and btrfs don't have to work out when they should use percpu_counter_sum() vs percpu_counter_sum_all() in their space accounting algorithms Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong

lib/percpu_counter: percpu_counter_add_batch() overflow/underflow

2023-02-03T06:50:01+00:00

Patch series "various irq handling fixes/docu updates". If an interrupt happens between __this_cpu_read(*fbc->counters) and this_cpu_add(*fbc->counters, amount), and that interrupt modifies the per_cpu_counter, then the this_cpu_add() after the interrupt returns may under/overflow. Link: https://lkml.kernel.org/r/20221216150155.200389-1-manfred@colorfullife.com Link: https://lkml.kernel.org/r/20221216150441.200533-1-manfred@colorfullife.com Signed-off-by: Manfred Spraul Cc: "Sun, Jiebin" Cc: <1vier1@web.de> Cc: Alexander Sverdlin Cc: Thomas Gleixner Signed-off-by: Andrew Morton

percpu_counter: add percpu_counter_sum_all interface

2022-11-30T23:58:40+00:00

The percpu_counter is used for scenarios where performance is more important than the accuracy. For percpu_counter users, who want more accurate information in their slowpath, percpu_counter_sum is provided which traverses all the online CPUs to accumulate the data. The reason it only needs to traverse online CPUs is because percpu_counter does implement CPU offline callback which syncs the local data of the offlined CPU. However there is a small race window between the online CPUs traversal of percpu_counter_sum and the CPU offline callback. The offline callback has to traverse all the percpu_counters on the system to flush the CPU local data which can be a lot. During that time, the CPU which is going offline has already been published as offline to all the readers. So, as the offline callback is running, percpu_counter_sum can be called for one counter which has some state on the CPU going offline. Since percpu_counter_sum only traverses online CPUs, it will skip that specific CPU and the offline callback might not have flushed the state for that specific percpu_counter on that offlined CPU. Normally this is not an issue because percpu_counter users can deal with some inaccuracy for small time window. However a new user i.e. mm_struct on the cleanup path wants to check the exact state of the percpu_counter through check_mm(). For such users, this patch introduces percpu_counter_sum_all() which traverses all possible CPUs and it is used in fork.c:check_mm() to avoid the potential race. This issue is exposed by the later patch "mm: convert mm's rss stats into percpu_counter". Link: https://lkml.kernel.org/r/20221109012011.881058-1-shakeelb@google.com Signed-off-by: Shakeel Butt Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski Signed-off-by: Andrew Morton

lib/percpu_counter: tame kernel-doc compile warning

2021-05-07T02:24:12+00:00

commit 3e8f399da490 ("writeback: rework wb_[dec|inc]_stat family of functions") add some function description of percpu_counter_add_batch. but the double '*' in comments means a kernel-doc format comment which isn't right. Since the whole file of lib/percpu_counter.c has no any other kernel-doc format comments, we'd better to remove this incomplete one to tame the kernel-doc warning: lib/percpu_counter.c:83: warning: Function parameter or member 'fbc' not described in 'percpu_counter_add_batch' lib/percpu_counter.c:83: warning: Function parameter or member 'amount' not described in 'percpu_counter_add_batch' lib/percpu_counter.c:83: warning: Function parameter or member 'batch' not described in 'percpu_counter_add_batch' Link: https://lkml.kernel.org/r/20210405135505.132446-1-alexs@kernel.org Signed-off-by: Alex Shi Cc: Nikolay Borisov Cc: Stephen Boyd Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

lib/percpu_counter.c: use helper macro abs()

2020-10-16T18:11:20+00:00

Use helper macro abs() to simplify the "x >= t || x <= -t" cmp. Signed-off-by: Miaohe Lin Signed-off-by: Andrew Morton Reviewed-by: Andrew Morton Link: https://lkml.kernel.org/r/20200927122746.5964-1-linmiaohe@huawei.com Signed-off-by: Linus Torvalds

treewide: Make all debug_obj_descriptors const

2020-09-24T19:56:25+00:00

This should make it harder for the kernel to corrupt the debug object descriptor, used to call functions to fixup state and track debug objects, by moving the structure to read-only memory. Signed-off-by: Stephen Boyd Signed-off-by: Thomas Gleixner Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20200815004027.2046113-3-swboyd@chromium.org

percpu_counter: add percpu_counter_sync()

2020-08-07T18:33:26+00:00

percpu_counter's accuracy is related to its batch size. For a percpu_counter with a big batch, its deviation could be big, so when the counter's batch is runtime changed to a smaller value for better accuracy, there could also be requirment to reduce the big deviation. So add a percpu-counter sync function to be run on each CPU. Reported-by: kernel test robot Signed-off-by: Feng Tang Signed-off-by: Andrew Morton Cc: Dennis Zhou Cc: Tejun Heo Cc: Christoph Lameter Cc: Michal Hocko Cc: Qian Cai Cc: Andi Kleen Cc: Huang Ying Cc: Dave Hansen Cc: Haiyang Zhang Cc: Johannes Weiner Cc: Kees Cook Cc: "K. Y. Srinivasan" Cc: Matthew Wilcox (Oracle) Cc: Mel Gorman Cc: Tim Chen Link: http://lkml.kernel.org/r/1594389708-60781-4-git-send-email-feng.tang@intel.com Signed-off-by: Linus Torvalds

notifier: Remove notifier header file wherever not used

2018-08-30T10:56:40+00:00

The conversion of the hotplug notifiers to a state machine left the notifier.h includes around in some places. Remove them. Signed-off-by: Mukesh Ojha Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/1535114033-4605-1-git-send-email-mojha@codeaurora.org