Messages in this thread | | | Subject | Re: [RFC V2 PATCH] kernfs: create raw version kernfs_path_len and kernfs_path | From | "Shi, Yang" <> | Date | Fri, 26 Feb 2016 15:05:07 -0800 |
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On 2/26/2016 3:01 PM, Greg KH wrote: > On Fri, Feb 26, 2016 at 01:47:39PM -0800, Yang Shi wrote: >> commit 5634cc2aa9aebc77bc862992e7805469dcf83dac ("writeback: update writeback >> tracepoints to report cgroup") made writeback tracepoints report cgroup >> writeback, but it may trigger the below bug on -rt kernel since kernfs_path >> and kernfs_path_len are called by tracepoints, which acquire sleeping lock. >> >> BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:930 >> in_atomic(): 1, irqs_disabled(): 0, pid: 625, name: kworker/u16:3 >> INFO: lockdep is turned off. >> Preemption disabled at:[<ffffffc000374a5c>] wb_writeback+0xec/0x830 >> >> CPU: 7 PID: 625 Comm: kworker/u16:3 Not tainted 4.4.1-rt5 #20 >> Hardware name: Freescale Layerscape 2085a RDB Board (DT) >> Workqueue: writeback wb_workfn (flush-7:0) >> Call trace: >> [<ffffffc00008d708>] dump_backtrace+0x0/0x200 >> [<ffffffc00008d92c>] show_stack+0x24/0x30 >> [<ffffffc0007b0f40>] dump_stack+0x88/0xa8 >> [<ffffffc000127d74>] ___might_sleep+0x2ec/0x300 >> [<ffffffc000d5d550>] rt_spin_lock+0x38/0xb8 >> [<ffffffc0003e0548>] kernfs_path_len+0x30/0x90 >> [<ffffffc00036b360>] trace_event_raw_event_writeback_work_class+0xe8/0x2e8 >> [<ffffffc000374f90>] wb_writeback+0x620/0x830 >> [<ffffffc000376224>] wb_workfn+0x61c/0x950 >> [<ffffffc000110adc>] process_one_work+0x3ac/0xb30 >> [<ffffffc0001112fc>] worker_thread+0x9c/0x7a8 >> [<ffffffc00011a9e8>] kthread+0x190/0x1b0 >> [<ffffffc000086ca0>] ret_from_fork+0x10/0x30 >> >> Since kernfs_* functions are heavily used by cgroup, so it sounds not >> reasonable to convert kernfs_rename_lock to raw lock. >> >> Call synchronize_sched() when kernfs_node is updated since tracepoints are >> protected by rcu_read_lock_sched. >> >> Create raw version kernfs_path, kernfs_path_len and cgroup_path, which don't >> acquire lock and are used by tracepoints only. >> >> Signed-off-by: Yang Shi <yang.shi@linaro.org> >> --- >> It should be applicable to both mainline and -rt kernel. >> The change survives ftrace stress test in ltp. >> >> v2: >> * Adopted Steven's suggestion to call synchronize_sched in kernfs_rename_ns. >> >> fs/kernfs/dir.c | 30 +++++++++++++++++++++++++++--- >> include/linux/cgroup.h | 10 ++++++++++ >> include/linux/kernfs.h | 10 ++++++++++ >> include/trace/events/writeback.h | 4 ++-- >> 4 files changed, 49 insertions(+), 5 deletions(-) >> >> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c >> index 996b774..70a9687 100644 >> --- a/fs/kernfs/dir.c >> +++ b/fs/kernfs/dir.c >> @@ -44,7 +44,7 @@ static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen) >> return strlcpy(buf, kn->parent ? kn->name : "/", buflen); >> } >> >> -static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf, >> +static char * __must_check __kernfs_path(struct kernfs_node *kn, char *buf, >> size_t buflen) >> { >> char *p = buf + buflen; >> @@ -131,12 +131,33 @@ char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen) >> char *p; >> >> spin_lock_irqsave(&kernfs_rename_lock, flags); >> - p = kernfs_path_locked(kn, buf, buflen); >> + p = __kernfs_path(kn, buf, buflen); >> spin_unlock_irqrestore(&kernfs_rename_lock, flags); >> return p; >> } >> EXPORT_SYMBOL_GPL(kernfs_path); >> >> +/* Raw version. Used by tracepoints only without acquiring lock */ >> +size_t _kernfs_path_len(struct kernfs_node *kn) >> +{ >> + size_t len = 0; >> + >> + do { >> + len += strlen(kn->name) + 1; >> + kn = kn->parent; >> + } while (kn && kn->parent); >> + >> + return len; >> +} >> + >> +char *_kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen) >> +{ >> + char *p; >> + >> + p = __kernfs_path(kn, buf, buflen); >> + return p; >> +} >> + >> /** >> * pr_cont_kernfs_name - pr_cont name of a kernfs_node >> * @kn: kernfs_node of interest >> @@ -168,7 +189,7 @@ void pr_cont_kernfs_path(struct kernfs_node *kn) >> >> spin_lock_irqsave(&kernfs_rename_lock, flags); >> >> - p = kernfs_path_locked(kn, kernfs_pr_cont_buf, >> + p = __kernfs_path(kn, kernfs_pr_cont_buf, >> sizeof(kernfs_pr_cont_buf)); >> if (p) >> pr_cont("%s", p); >> @@ -1397,6 +1418,9 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent, >> kn->hash = kernfs_name_hash(kn->name, kn->ns); >> kernfs_link_sibling(kn); >> >> + /* Tracepoints are protected by rcu_read_lock_sched */ >> + synchronize_sched(); >> + >> kernfs_put(old_parent); >> kfree_const(old_name); >> >> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h >> index 2162dca..bbd88d3 100644 >> --- a/include/linux/cgroup.h >> +++ b/include/linux/cgroup.h >> @@ -538,6 +538,16 @@ static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf, >> return kernfs_path(cgrp->kn, buf, buflen); >> } >> >> +/* >> + * Without acquiring kernfs_rename_lock in _kernfs_path. >> + * Used by tracepoints only. >> + */ >> +static inline char * __must_check _cgroup_path(struct cgroup *cgrp, char *buf, >> + size_t buflen) >> +{ >> + return _kernfs_path(cgrp->kn, buf, buflen); >> +} >> + >> static inline void pr_cont_cgroup_name(struct cgroup *cgrp) >> { >> pr_cont_kernfs_name(cgrp->kn); >> diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h >> index af51df3..14c01cdc 100644 >> --- a/include/linux/kernfs.h >> +++ b/include/linux/kernfs.h >> @@ -267,8 +267,11 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn) >> >> int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen); >> size_t kernfs_path_len(struct kernfs_node *kn); >> +size_t _kernfs_path_len(struct kernfs_node *kn); >> char * __must_check kernfs_path(struct kernfs_node *kn, char *buf, >> size_t buflen); >> +char * __must_check _kernfs_path(struct kernfs_node *kn, char *buf, >> + size_t buflen); > > I despise functions with just a _ in the front of them, you don't give > anyone a clue as to what they are for, or why to use one vs. the other. > Trust me, you will not remember it either in 1 month, let alone 5 years. > > Please change the whole function name to be obvious as to what to use, > or not use.
How about kernfs_*_unlocked() for raw version? And, keep lock version name intact?
Thanks, Yang
> > thanks, > > greg k-h >
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