kernel/linux.git/fs/proc/base.c, branch linux-6.0.y

proc: fix a dentry lock race between release_task and lookup

2022-07-18T00:31:43+00:00

Commit 7bc3e6e55acf06 ("proc: Use a list of inodes to flush from proc") moved proc_flush_task() behind __exit_signal(). Then, process systemd can take long period high cpu usage during releasing task in following concurrent processes: systemd ps kernel_waitid stat(/proc/tgid) do_wait filename_lookup wait_consider_task lookup_fast release_task __exit_signal __unhash_process detach_pid __change_pid // remove task->pid_links d_revalidate -> pid_revalidate // 0 d_invalidate(/proc/tgid) shrink_dcache_parent(/proc/tgid) d_walk(/proc/tgid) spin_lock_nested(/proc/tgid/fd) // iterating opened fd proc_flush_pid | d_invalidate (/proc/tgid/fd) | shrink_dcache_parent(/proc/tgid/fd) | shrink_dentry_list(subdirs) ↓ shrink_lock_dentry(/proc/tgid/fd) --> race on dentry lock Function d_invalidate() will remove dentry from hash firstly, but why does proc_flush_pid() process dentry '/proc/tgid/fd' before dentry '/proc/tgid'? That's because proc_pid_make_inode() adds proc inode in reverse order by invoking hlist_add_head_rcu(). But proc should not add any inodes under '/proc/tgid' except '/proc/tgid/task/pid', fix it by adding inode into 'pid->inodes' only if the inode is /proc/tgid or /proc/tgid/task/pid. Performance regression: Create 200 tasks, each task open one file for 50,000 times. Kill all tasks when opened files exceed 10,000,000 (cat /proc/sys/fs/file-nr). Before fix: $ time killall -wq aa real 4m40.946s # During this period, we can see 'ps' and 'systemd' taking high cpu usage. After fix: $ time killall -wq aa real 1m20.732s # During this period, we can see 'systemd' taking high cpu usage. Link: https://lkml.kernel.org/r/20220713130029.4133533-1-chengzhihao1@huawei.com Fixes: 7bc3e6e55acf06 ("proc: Use a list of inodes to flush from proc") Link: https://bugzilla.kernel.org/show_bug.cgi?id=216054 Signed-off-by: Zhihao Cheng Signed-off-by: Zhang Yi Suggested-by: Brian Foster Reviewed-by: Brian Foster Cc: Al Viro Cc: Alexey Dobriyan Cc: Eric Biederman Cc: Matthew Wilcox Cc: Baoquan He Cc: Kalesh Singh Cc: Yu Kuai Signed-off-by: Andrew Morton

ksm: count ksm merging pages for each process

2022-04-29T06:16:16+00:00

Some applications or containers want to use KSM by calling madvise() to advise areas of address space to be MERGEABLE. But they may not know which applications are more likely to cause real merges in the deployment. If this patch is applied, it helps them know their corresponding number of merged pages, and then optimize their app code. As current KSM only counts the number of KSM merging pages(e.g. ksm_pages_sharing and ksm_pages_shared) of the whole system, we cannot see the more fine-grained KSM merging, for the upper application optimization, the merging area cannot be set easily according to the KSM page merging probability of each process. Therefore, it is necessary to add extra statistical means so that the upper level users can know the detailed KSM merging information of each process. We add a new proc file named as ksm_merging_pages under /proc// to indicate the involved ksm merging pages of this process. [akpm@linux-foundation.org: fix comment typo, remove BUG_ON()s] Link: https://lkml.kernel.org/r/20220325082318.2352853-1-xu.xin16@zte.com.cn Signed-off-by: xu xin Reported-by: kernel test robot Reviewed-by: Yang Yang Reviewed-by: Ran Xiaokai Reported-by: Zeal Robot Cc: Kees Cook Cc: Alexey Dobriyan Cc: Stephen Rothwell Cc: Ohhoon Kwon Cc: Matthew Wilcox (Oracle) Cc: Stephen Brennan Cc: Vlastimil Babka Cc: Feng Tang Cc: Yang Yang Cc: Ran Xiaokai Cc: Zeal Robot Signed-off-by: Andrew Morton

Merge tag 'ptrace-cleanups-for-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2022-03-29T00:29:53+00:00

Pull ptrace cleanups from Eric Biederman: "This set of changes removes tracehook.h, moves modification of all of the ptrace fields inside of siglock to remove races, adds a missing permission check to ptrace.c The removal of tracehook.h is quite significant as it has been a major source of confusion in recent years. Much of that confusion was around task_work and TIF_NOTIFY_SIGNAL (which I have now decoupled making the semantics clearer). For people who don't know tracehook.h is a vestiage of an attempt to implement uprobes like functionality that was never fully merged, and was later superseeded by uprobes when uprobes was merged. For many years now we have been removing what tracehook functionaly a little bit at a time. To the point where anything left in tracehook.h was some weird strange thing that was difficult to understand" * tag 'ptrace-cleanups-for-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: ptrace: Remove duplicated include in ptrace.c ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE ptrace: Return the signal to continue with from ptrace_stop ptrace: Move setting/clearing ptrace_message into ptrace_stop tracehook: Remove tracehook.h resume_user_mode: Move to resume_user_mode.h resume_user_mode: Remove #ifdef TIF_NOTIFY_RESUME in set_notify_resume signal: Move set_notify_signal and clear_notify_signal into sched/signal.h task_work: Decouple TIF_NOTIFY_SIGNAL and task_work task_work: Call tracehook_notify_signal from get_signal on all architectures task_work: Introduce task_work_pending task_work: Remove unnecessary include from posix_timers.h ptrace: Remove tracehook_signal_handler ptrace: Remove arch_syscall_{enter,exit}_tracehook ptrace: Create ptrace_report_syscall_{entry,exit} in ptrace.h ptrace/arm: Rename tracehook_report_syscall report_syscall ptrace: Move ptrace_report_syscall into ptrace.h

proc: alloc PATH_MAX bytes for /proc/${pid}/fd/ symlinks

2022-03-24T02:00:33+00:00

It's not a standard approach that use __get_free_page() to alloc path buffer directly. We'd better use kmalloc and PATH_MAX. PAGE_SIZE is different on different archs. An unlinked file with very long canonical pathname will readlink differently because "(deleted)" eats into a buffer. --adobriyan [akpm@linux-foundation.org: remove now-unneeded cast] Link: https://lkml.kernel.org/r/Ye1fCxyZZ0I5lgOL@localhost.localdomain Signed-off-by: Hao Lee Signed-off-by: Alexey Dobriyan Cc: Christian Brauner Cc: Kees Cook Cc: James Morris Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

tracehook: Remove tracehook.h

2022-03-10T22:51:51+00:00

Now that all of the definitions have moved out of tracehook.h into ptrace.h, sched/signal.h, resume_user_mode.h there is nothing left in tracehook.h so remove it. Update the few files that were depending upon tracehook.h to bring in definitions to use the headers they need directly. Reviewed-by: Kees Cook Link: https://lkml.kernel.org/r/20220309162454.123006-13-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"

proc: convert the return type of proc_fd_access_allowed() to be boolean

2022-01-20T06:52:52+00:00

Convert return type of proc_fd_access_allowed() and the 'allowed' in it to be boolean since the return type of ptrace_may_access() is boolean. Link: https://lkml.kernel.org/r/20211219024404.29779-1-zhengqi.arch@bytedance.com Signed-off-by: Qi Zheng Cc: Kees Cook Cc: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'akpm' (patches from Andrew)

2021-11-09T18:11:53+00:00

Merge more updates from Andrew Morton: "87 patches. Subsystems affected by this patch series: mm (pagecache and hugetlb), procfs, misc, MAINTAINERS, lib, checkpatch, binfmt, kallsyms, ramfs, init, codafs, nilfs2, hfs, crash_dump, signals, seq_file, fork, sysvfs, kcov, gdb, resource, selftests, and ipc" * emailed patches from Andrew Morton : (87 commits) ipc/ipc_sysctl.c: remove fallback for !CONFIG_PROC_SYSCTL ipc: check checkpoint_restore_ns_capable() to modify C/R proc files selftests/kselftest/runner/run_one(): allow running non-executable files virtio-mem: disallow mapping virtio-mem memory via /dev/mem kernel/resource: disallow access to exclusive system RAM regions kernel/resource: clean up and optimize iomem_is_exclusive() scripts/gdb: handle split debug for vmlinux kcov: replace local_irq_save() with a local_lock_t kcov: avoid enable+disable interrupts if !in_task() kcov: allocate per-CPU memory on the relevant node Documentation/kcov: define `ip' in the example Documentation/kcov: include types.h in the example sysv: use BUILD_BUG_ON instead of runtime check kernel/fork.c: unshare(): use swap() to make code cleaner seq_file: fix passing wrong private data seq_file: move seq_escape() to a header signal: remove duplicate include in signal.h crash_dump: remove duplicate include in crash_dump.h crash_dump: fix boolreturn.cocci warning hfs/hfsplus: use WARN_ON for sanity check ...

proc: allow pid_revalidate() during LOOKUP_RCU

2021-11-09T18:02:49+00:00

Problem Description: When running running ~128 parallel instances of TZ=/etc/localtime ps -fe >/dev/null on a 128CPU machine, the %sys utilization reaches 97%, and perf shows the following code path as being responsible for heavy contention on the d_lockref spinlock: walk_component() lookup_fast() d_revalidate() pid_revalidate() // returns -ECHILD unlazy_child() lockref_get_not_dead(&nd->path.dentry->d_lockref) <-- contention The reason is that pid_revalidate() is triggering a drop from RCU to ref path walk mode. All concurrent path lookups thus try to grab a reference to the dentry for /proc/, before re-executing pid_revalidate() and then stepping into the /proc/$pid directory. Thus there is huge spinlock contention. This patch allows pid_revalidate() to execute in RCU mode, meaning that the path lookup can successfully enter the /proc/$pid directory while still in RCU mode. Later on, the path lookup may still drop into ref mode, but the contention will be much reduced at this point. By applying this patch, %sys utilization falls to around 85% under the same workload, and the number of ps processes executed per unit time increases by 3x-4x. Although this particular workload is a bit contrived, we have seen some large collections of eager monitoring scripts which produced similarly high %sys time due to contention in the /proc directory. As a result this patch, Al noted that several procfs methods which were only called in ref-walk mode could now be called from RCU mode. To ensure that this patch is safe, I audited all the inode get_link and permission() implementations, as well as dentry d_revalidate() implementations, in fs/proc. The purpose here is to ensure that they either are safe to call in RCU (i.e. don't sleep) or correctly bail out of RCU mode if they don't support it. My analysis shows that all at-risk procfs methods are safe to call under RCU, and thus this patch is safe. Procfs RCU-walk Analysis: This analysis is up-to-date with 5.15-rc3. When called under RCU mode, these functions have arguments as follows: * get_link() receives a NULL dentry pointer when called in RCU mode. * permission() receives MAY_NOT_BLOCK in the mode parameter when called from RCU. * d_revalidate() receives LOOKUP_RCU in flags. For the following functions, either they are trivially RCU safe, or they explicitly bail at the beginning of the function when they run: proc_ns_get_link (bails out) proc_get_link (RCU safe) proc_pid_get_link (bails out) map_files_d_revalidate (bails out) map_misc_d_revalidate (bails out) proc_net_d_revalidate (RCU safe) proc_sys_revalidate (bails out, also not under /proc/$pid) tid_fd_revalidate (bails out) proc_sys_permission (not under /proc/$pid) The remainder of the functions require a bit more detail: * proc_fd_permission: RCU safe. All of the body of this function is under rcu_read_lock(), except generic_permission() which declares itself RCU safe in its documentation string. * proc_self_get_link uses GFP_ATOMIC in the RCU case, so it is RCU aware and otherwise looks safe. The same is true of proc_thread_self_get_link. * proc_map_files_get_link: calls ns_capable, which calls capable(), and thus calls into the audit code (see note #1 below). The remainder is just a call to the trivially safe proc_pid_get_link(). * proc_pid_permission: calls ptrace_may_access(), which appears RCU safe, although it does call into the "security_ptrace_access_check()" hook, which looks safe under smack and selinux. Just the audit code is of concern. Also uses get_task_struct() and put_task_struct(), see note #2 below. * proc_tid_comm_permission: Appears safe, though calls put_task_struct (see note #2 below). Note #1: Most of the concern of RCU safety has centered around the audit code. However, since b17ec22fb339 ("selinux: slow_avc_audit has become non-blocking"), it's safe to call this code under RCU. So all of the above are safe by my estimation. Note #2: get_task_struct() and put_task_struct(): The majority of get_task_struct() is under RCU read lock, and in any case it is a simple increment. But put_task_struct() is complex, given that it could at some point free the task struct, and this process has many steps which I couldn't manually verify. However, several other places call put_task_struct() under RCU, so it appears safe to use here too (see kernel/hung_task.c:165 or rcu/tree-stall.h:296) Patch description: pid_revalidate() drops from RCU into REF lookup mode. When many threads are resolving paths within /proc in parallel, this can result in heavy spinlock contention on d_lockref as each thread tries to grab a reference to the /proc dentry (and drop it shortly thereafter). Investigation indicates that it is not necessary to drop RCU in pid_revalidate(), as no RCU data is modified and the function never sleeps. So, remove the LOOKUP_RCU check. Link: https://lkml.kernel.org/r/20211004175629.292270-2-stephen.s.brennan@oracle.com Signed-off-by: Stephen Brennan Cc: Konrad Wilk Cc: Alexander Viro Cc: Matthew Wilcox Cc: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

procfs: do not list TID 0 in /proc//task

2021-11-09T18:02:48+00:00

If a task exits concurrently, task_pid_nr_ns may return 0. [akpm@linux-foundation.org: coding style tweaks] [adobriyan@gmail.com: test that /proc/*/task doesn't contain "0"] Link: https://lkml.kernel.org/r/YV88AnVzHxPafQ9o@localhost.localdomain Link: https://lkml.kernel.org/r/8735pn5dx7.fsf@oldenburg.str.redhat.com Signed-off-by: Florian Weimer Signed-off-by: Alexey Dobriyan Acked-by: Christian Brauner Reviewed-by: Alexey Dobriyan Cc: Kees Cook Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Revert "proc/wchan: use printk format instead of lookup_symbol_name()"

2021-10-15T09:25:13+00:00

This reverts commit 152c432b128cb043fc107e8f211195fe94b2159c. When a kernel address couldn't be symbolized for /proc/$pid/wchan, it would leak the raw value, a potential information exposure. This is a regression compared to the safer pre-v5.12 behavior. Reported-by: kernel test robot Reported-by: Vito Caputo Reported-by: Jann Horn Signed-off-by: Kees Cook Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20211008111626.090829198@infradead.org