tracing/user_events: Align set_bit() address for all archs

All architectures should use a long aligned address passed to set_bit().
User processes can pass either a 32-bit or 64-bit sized value to b

tracing/user_events: Align set_bit() address for all archs

All architectures should use a long aligned address passed to set_bit().
User processes can pass either a 32-bit or 64-bit sized value to be
updated when tracing is enabled when on a 64-bit kernel. Both cases are
ensured to be naturally aligned, however, that is not enough. The
address must be long aligned without affecting checks on the value
within the user process which require different adjustments for the bit
for little and big endian CPUs.

Add a compat flag to user_event_enabler that indicates when a 32-bit
value is being used on a 64-bit kernel. Long align addresses and correct
the bit to be used by set_bit() to account for this alignment. Ensure
compat flags are copied during forks and used during deletion clears.

Link: https://lore.kernel.org/linux-trace-kernel/20230925230829.341-2-beaub@linux.microsoft.com
Link: https://lore.kernel.org/linux-trace-kernel/20230914131102.179100-1-cleger@rivosinc.com/

Cc: stable@vger.kernel.org
Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event enablement")
Reported-by: Clément Léger <cleger@rivosinc.com>
Suggested-by: Clément Léger <cleger@rivosinc.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

show more ...

tracing/user_events: Optimize safe list traversals

Several of the list traversals in the user_events facility use safe list
traversals where they could be using the unsafe versions instead.

Replace

tracing/user_events: Optimize safe list traversals

Several of the list traversals in the user_events facility use safe list
traversals where they could be using the unsafe versions instead.

Replace these safe traversals with their unsafe counterparts in the
interest of optimization.

Link: https://lore.kernel.org/linux-trace-kernel/20230810194337.695983-1-ervaughn@linux.microsoft.com

Suggested-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Eric Vaughn <ervaughn@linux.microsoft.com>
Acked-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Fix struct arg size match check

When users register an event the name of the event and it's argument are
checked to ensure they match if the event already exists. Normally all
a

tracing/user_events: Fix struct arg size match check

When users register an event the name of the event and it's argument are
checked to ensure they match if the event already exists. Normally all
arguments are in the form of "type name", except for when the type
starts with "struct ". In those cases, the size of the struct is passed
in addition to the name, IE: "struct my_struct a 20" for an argument
that is of type "struct my_struct" with a field name of "a" and has the
size of 20 bytes.

The current code does not honor the above case properly when comparing
a match. This causes the event register to fail even when the same
string was used for events that contain a struct argument within them.
The example above "struct my_struct a 20" generates a match string of
"struct my_struct a" omitting the size field.

Add the struct size of the existing field when generating a comparison
string for a struct field to ensure proper match checking.

Link: https://lkml.kernel.org/r/20230629235049.581-2-beaub@linux.microsoft.com

Cc: stable@vger.kernel.org
Fixes: e6f89a149872 ("tracing/user_events: Ensure user provided strings are safely formatted")
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Fix incorrect return value for writing operation when events are disabled

The writing operation return the count of writes regardless of whether events
are enabled or disabled.

tracing/user_events: Fix incorrect return value for writing operation when events are disabled

The writing operation return the count of writes regardless of whether events
are enabled or disabled. Switch it to return -EBADF to indicates that the event
is disabled.

Link: https://lkml.kernel.org/r/20230626111344.19136-2-sunliming@kylinos.cn

Cc: stable@vger.kernel.org
7f5a08c79df35 ("user_events: Add minimal support for trace_event into ftrace")
Acked-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: sunliming <sunliming@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Add auto cleanup and future persist flag

Currently user events need to be manually deleted via the delete IOCTL
call or via the dynamic_events file. Most operators and processes

tracing/user_events: Add auto cleanup and future persist flag

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 <rostedt@goodmis.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Track refcount consistently via put/get

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 behavio

tracing/user_events: Track refcount consistently via put/get

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 <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Store register flags on events

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
th

tracing/user_events: Store register flags on events

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 <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Remove user_ns walk for groups

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
th

tracing/user_events: Remove user_ns walk for groups

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 <brauner@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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

The user_events support events that has empty arguments. But the trace event
is discarded and not really committed when

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

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 <beaub@linux.microsoft.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: sunliming <sunliming@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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

When A registering user event from dyn_events has no argments, it will pass the
matching check, regardless of whether ther

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

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 <sunliming@kylinos.cn>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Prevent same name but different args event

User processes register name_args for events. If the same name but different
args event are registered. The trace outputs of second ev

tracing/user_events: Prevent same name but different args event

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 <sunliming@kylinos.cn>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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mm/gup: remove unused vmas parameter from pin_user_pages_remote()

No invocation of pin_user_pages_remote() uses the vmas parameter, so
remove it. This forms part of a larger patch set eliminating t

mm/gup: remove unused vmas parameter from pin_user_pages_remote()

No invocation of pin_user_pages_remote() uses the vmas parameter, so
remove it. This forms part of a larger patch set eliminating the use of
the vmas parameters altogether.

Link: https://lkml.kernel.org/r/28f000beb81e45bf538a2aaa77c90f5482b67a32.1684350871.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

tracing/user_events: Document user_event_mm one-shot list usage

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 no

tracing/user_events: Document user_event_mm one-shot list usage

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 <torvalds@linux-foundation.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Rename link fields for clarity

Currently most list_head fields of various structs within user_events
are simply named link. This causes folks to keep additional context in
their

tracing/user_events: Rename link fields for clarity

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 <torvalds@linux-foundation.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Remove RCU lock while pinning pages

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
t

tracing/user_events: Remove RCU lock while pinning pages

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 <torvalds@linux-foundation.org>
[ change log written by Beau Belgrave ]
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Split up mm alloc and attach

When a new mm is being created in a fork() path it currently is
allocated and then attached in one go. This leaves the mm exposed out to
the tracing

tracing/user_events: Split up mm alloc and attach

When a new mm is being created in a fork() path it currently is
allocated and then attached in one go. This leaves the mm exposed out to
the tracing register callbacks while any parent enabler locations are
copied in. This should not happen.

Split up mm alloc and attach as unique operations. When duplicating
enablers, first alloc, then duplicate, and only upon success, attach.
This prevents any timing window outside of the event_reg mutex for
enablement walking. This allows for dropping RCU requirement for
enablement walking in later patches.

Link: https://lkml.kernel.org/r/20230519230741.669-2-beaub@linux.microsoft.com
Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=whTBvXJuoi_kACo3qi5WZUmRrhyA-_=rRFsycTytmB6qw@mail.gmail.com/

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ change log written by Beau Belgrave ]
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Use long vs int for atomic bit ops

Each event stores a int to track which bit to set/clear when enablement
changes. On big endian 64-bit configurations, it's possible this could

tracing/user_events: Use long vs int for atomic bit ops

Each event stores a int to track which bit to set/clear when enablement
changes. On big endian 64-bit configurations, it's possible this could
cause memory corruption when it's used for atomic bit operations.

Use unsigned long for enablement values to ensure any possible
corruption cannot occur. Downcast to int after mask for the bit target.

Link: https://lore.kernel.org/all/6f758683-4e5e-41c3-9b05-9efc703e827c@kili.mountain/
Link: https://lore.kernel.org/linux-trace-kernel/20230505205855.6407-1-beaub@linux.microsoft.com

Fixes: dcb8177c1395 ("tracing/user_events: Add ioctl for disabling addresses")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Limit max fault-in attempts

When event enablement changes, user_events attempts to update a bit in
the user process. If a fault is hit, an attempt to fault-in the page and
the w

tracing/user_events: Limit max fault-in attempts

When event enablement changes, user_events attempts to update a bit in
the user process. If a fault is hit, an attempt to fault-in the page and
the write is retried if the page made it in. While this normally requires
a couple attempts, it is possible a bad user process could attempt to
cause infinite loops.

Ensure fault-in attempts either sync or async are limited to a max of 10
attempts for each update. When the max is hit, return -EFAULT so another
attempt is not made in all cases.

Link: https://lkml.kernel.org/r/20230425225107.8525-5-beaub@linux.microsoft.com

Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

show more ...

tracing/user_events: Prevent same address and bit per process

User processes register an address and bit pair for events. If the same
address and bit pair are registered multiple times in the same p

tracing/user_events: Prevent same address and bit per process

User processes register an address and bit pair for events. If the same
address and bit pair are registered multiple times in the same process,
it can cause undefined behavior when events are enabled/disabled.
When more than one are used, the bit could be turned off by another
event being disabled, while the original event is still enabled.

Prevent undefined behavior by checking the current mm to see if any
event has already been registered for the address and bit pair. Return
EADDRINUSE back to the user process if it's already being used.

Update ftrace self-test to ensure this occurs properly.

Link: https://lkml.kernel.org/r/20230425225107.8525-4-beaub@linux.microsoft.com

Suggested-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Ensure bit is cleared on unregister

If an event is enabled and a user process unregisters user_events, the
bit is left set. Fix this by always clearing the bit in the user proce

tracing/user_events: Ensure bit is cleared on unregister

If an event is enabled and a user process unregisters user_events, the
bit is left set. Fix this by always clearing the bit in the user process
if unregister is successful.

Update abi self-test to ensure this occurs properly.

Link: https://lkml.kernel.org/r/20230425225107.8525-3-beaub@linux.microsoft.com

Suggested-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Ensure write index cannot be negative

The write index indicates which event the data is for and accesses a
per-file array. The index is passed by user processes during write()
c

tracing/user_events: Ensure write index cannot be negative

The write index indicates which event the data is for and accesses a
per-file array. The index is passed by user processes during write()
calls as the first 4 bytes. Ensure that it cannot be negative by
returning -EINVAL to prevent out of bounds accesses.

Update ftrace self-test to ensure this occurs properly.

Link: https://lkml.kernel.org/r/20230425225107.8525-2-beaub@linux.microsoft.com

Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace")
Reported-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Set event filter_type from type

Users expect that events can be filtered by the kernel. User events
currently sets all event fields as FILTER_OTHER which limits to binary
filter

tracing/user_events: Set event filter_type from type

Users expect that events can be filtered by the kernel. User events
currently sets all event fields as FILTER_OTHER which limits to binary
filters only. When strings are being used, functionality is reduced.

Use filter_assign_type() to find the most appropriate filter
type for each field in user events to ensure full kernel capabilities.

Link: https://lkml.kernel.org/r/20230419214140.4158-2-beaub@linux.microsoft.com

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

show more ...

tracing/user_events: Use print_format_fields() for trace output

Currently, user events are shown using the "hex" output for "safety"
reasons as one cannot trust user events behaving nicely. But the

tracing/user_events: Use print_format_fields() for trace output

Currently, user events are shown using the "hex" output for "safety"
reasons as one cannot trust user events behaving nicely. But the hex
output is not the only utility for safe outputting of trace events. The
print_event_fields() is just as safe and gives user readable output.

Before:
example-839 [001] ..... 43.222244:
00000000: b1 06 00 00 47 03 00 00 00 00 00 00 ....G.......
example-839 [001] ..... 43.564433:
00000000: b1 06 00 00 47 03 00 00 01 00 00 00 ....G.......
example-839 [001] ..... 43.763917:
00000000: b1 06 00 00 47 03 00 00 02 00 00 00 ....G.......
example-839 [001] ..... 43.967929:
00000000: b1 06 00 00 47 03 00 00 03 00 00 00 ....G.......

After:

example-837 [006] ..... 55.739249: test: count=0x0 (0)
example-837 [006] ..... 111.104784: test: count=0x1 (1)
example-837 [006] ..... 111.268444: test: count=0x2 (2)
example-837 [006] ..... 111.416533: test: count=0x3 (3)
example-837 [006] ..... 111.542859: test: count=0x4 (4)

Link: https://lore.kernel.org/linux-trace-kernel/20230328151413.4770b8d7@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Align structs with tabs for readability

Add tabs to make struct members easier to read and unify the style of
the code.

Link: https://lkml.kernel.org/r/20230328235219.203-13-be

tracing/user_events: Align structs with tabs for readability

Add tabs to make struct members easier to read and unify the style of
the code.

Link: https://lkml.kernel.org/r/20230328235219.203-13-beaub@linux.microsoft.com

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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tracing/user_events: Limit global user_event count

Operators want to be able to ensure enough tracepoints exist on the
system for kernel components as well as for user components. Since there
are on

tracing/user_events: Limit global user_event count

Operators want to be able to ensure enough tracepoints exist on the
system for kernel components as well as for user components. Since there
are only up to 64K events, by default allow up to half to be used by
user events.

Add a kernel sysctl parameter (kernel.user_events_max) to set a global
limit that is honored among all groups on the system. This ensures hard
limits can be setup to prevent user processes from consuming all event
IDs on the system.

Link: https://lkml.kernel.org/r/20230328235219.203-12-beaub@linux.microsoft.com

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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