linux/kernel/trace/trace_events_user.c, branch v6.4

tracing/user_events: Add auto cleanup and future persist flag

2023-06-14T17:43:27Z

Currently user events need to be manually deleted via the delete IOCTL call or via the dynamic_events file. Most operators and processes wish to have these events auto cleanup when they are no longer used by anything to prevent them piling without manual maintenance. However, some operators may not want this, such as pre-registering events via the dynamic_events tracefs file. Update user_event_put() to attempt an auto delete of the event if it's the last reference. The auto delete must run in a work queue to ensure proper behavior of class->reg() invocations that don't expect the call to go away from underneath them during the unregister. Add work_struct to user_event struct to ensure we can do this reliably. Add a persist flag, that is not yet exposed, to ensure we can toggle between auto-cleanup and leaving the events existing in the future. When a non-zero flag is seen during register, return -EINVAL to ensure ABI is clear for the user processes while we work out the best approach for persistent events. Link: https://lkml.kernel.org/r/20230614163336.5797-4-beaub@linux.microsoft.com Link: https://lore.kernel.org/linux-trace-kernel/20230518093600.3f119d68@rorschach.local.home/ Suggested-by: Steven Rostedt Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Track refcount consistently via put/get

2023-06-14T17:43:26Z

Various parts of the code today track user_event's refcnt field directly via a refcount_add/dec. This makes it hard to modify the behavior of the last reference decrement in all code paths consistently. For example, in the future we will auto-delete events upon the last reference going away. This last reference could happen in many places, but we want it to be consistently handled. Add user_event_get() and user_event_put() for the add/dec. Update all places where direct refcounts are being used to utilize these new functions. In each location pass if event_mutex is locked or not. This allows us to drop events automatically in future patches clearly. Ensure when caller states the lock is held, it really is (or is not) held. Link: https://lkml.kernel.org/r/20230614163336.5797-3-beaub@linux.microsoft.com Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Store register flags on events

2023-06-14T17:43:26Z

Currently we don't have any available flags for user processes to use to indicate options for user_events. We will soon have a flag to indicate the event should or should not auto-delete once it's not being used by anyone. Add a reg_flags field to user_events and parameters to existing functions to allow for this in future patches. Link: https://lkml.kernel.org/r/20230614163336.5797-2-beaub@linux.microsoft.com Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Remove user_ns walk for groups

2023-06-14T16:41:53Z

During discussions it was suggested that user_ns is not a good place to try to attach a tracing namespace. The current code has stubs to enable that work that are very likely to change and incur a performance cost. Remove the user_ns walk when creating a group and determining the system name to use, since it's unlikely user_ns will be used in the future. Link: https://lore.kernel.org/all/20230601-urenkel-holzofen-cd9403b9cadd@brauner/ Link: https://lore.kernel.org/linux-trace-kernel/20230601224928.301-1-beaub@linux.microsoft.com Suggested-by: Christian Brauner Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Fix the incorrect trace record for empty arguments events

2023-06-14T16:41:52Z

The user_events support events that has empty arguments. But the trace event is discarded and not really committed when the arguments is empty. Fix this by not attempting to copy in zero-length data. Link: https://lkml.kernel.org/r/20230606062027.1008398-2-sunliming@kylinos.cn Acked-by: Beau Belgrave Acked-by: Masami Hiramatsu (Google) Signed-off-by: sunliming Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Handle matching arguments that is null from dyn_events

2023-06-14T16:41:52Z

When A registering user event from dyn_events has no argments, it will pass the matching check, regardless of whether there is a user event with the same name and arguments. Add the matching check when the arguments of registering user event is null. Link: https://lore.kernel.org/linux-trace-kernel/20230529065110.303440-1-sunliming@kylinos.cn Signed-off-by: sunliming Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Prevent same name but different args event

2023-06-14T16:41:52Z

User processes register name_args for events. If the same name but different args event are registered. The trace outputs of second event are printed as the first event. This is incorrect. Return EADDRINUSE back to the user process if the same name but different args event has being registered. Link: https://lore.kernel.org/linux-trace-kernel/20230529032100.286534-1-sunliming@kylinos.cn Signed-off-by: sunliming Reviewed-by: Masami Hiramatsu (Google) Acked-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Document user_event_mm one-shot list usage

2023-05-24T01:08:33Z

During 6.4 development it became clear that the one-shot list used by the user_event_mm's next field was confusing to others. It is not clear how this list is protected or what the next field usage is for unless you are familiar with the code. Add comments into the user_event_mm struct indicating lock requirement and usage. Also document how and why this approach was used via comments in both user_event_enabler_update() and user_event_mm_get_all() and the rules to properly use it. Link: https://lkml.kernel.org/r/20230519230741.669-5-beaub@linux.microsoft.com Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wicngggxVpbnrYHjRTwGE0WYscPRM+L2HO2BF8ia1EXgQ@mail.gmail.com/ Suggested-by: Linus Torvalds Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Rename link fields for clarity

2023-05-24T01:08:33Z

Currently most list_head fields of various structs within user_events are simply named link. This causes folks to keep additional context in their head when working with the code, which can be confusing. Instead of using link, describe what the actual link is, for example: list_del_rcu(&mm->link); Changes into: list_del_rcu(&mm->mms_link); The reader now is given a hint the link is to the mms global list instead of having to remember or spot check within the code. Link: https://lkml.kernel.org/r/20230519230741.669-4-beaub@linux.microsoft.com Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wicngggxVpbnrYHjRTwGE0WYscPRM+L2HO2BF8ia1EXgQ@mail.gmail.com/ Suggested-by: Linus Torvalds Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)

tracing/user_events: Remove RCU lock while pinning pages

2023-05-24T01:05:04Z

pin_user_pages_remote() can reschedule which means we cannot hold any RCU lock while using it. Now that enablers are not exposed out to the tracing register callbacks during fork(), there is clearly no need to require the RCU lock as event_mutex is enough to protect changes. Remove unneeded RCU usages when pinning pages and walking enablers with event_mutex held. Cleanup a misleading "safe" list walk that is not needed. During fork() duplication, remove unneeded RCU list add, since the list is not exposed yet. Link: https://lkml.kernel.org/r/20230519230741.669-3-beaub@linux.microsoft.com Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wiiBfT4zNS29jA0XEsy8EmbqTH1hAPdRJCDAJMD8Gxt5A@mail.gmail.com/ Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event enablement") Signed-off-by: Linus Torvalds [ change log written by Beau Belgrave ] Signed-off-by: Beau Belgrave Signed-off-by: Steven Rostedt (Google)