linux/kernel/trace/ring_buffer.c, branch v4.19

ring-buffer: Allow for rescheduling when removing pages

2018-09-17T22:15:11Z

When reducing ring buffer size, pages are removed by scheduling a work item on each CPU for the corresponding CPU ring buffer. After the pages are removed from ring buffer linked list, the pages are free()d in a tight loop. The loop does not give up CPU until all pages are removed. In a worst case behavior, when lot of pages are to be freed, it can cause system stall. After the pages are removed from the list, the free() can happen while the work is rescheduled. Call cond_resched() in the loop to prevent the system hangup. Link: http://lkml.kernel.org/r/20180907223129.71994-1-vnagarnaik@google.com Cc: stable@vger.kernel.org Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic") Reported-by: Jason Behmer Signed-off-by: Vaibhav Nagarnaik Signed-off-by: Steven Rostedt (VMware)

tracing: Add SPDX License format tags to tracing files

2018-08-16T23:08:06Z

Add the SPDX License header to ease license compliance management. Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Make ring_buffer_record_is_set_on() return bool

2018-08-02T01:09:50Z

The value of ring_buffer_record_is_set_on() is either true or false, so have its return value be bool. Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Make ring_buffer_record_is_on() return bool

2018-08-02T01:08:30Z

The value of ring_buffer_record_is_on() is either true or false, so have its return value be bool. Signed-off-by: Steven Rostedt (VMware)

ring_buffer: tracing: Inherit the tracing setting to next ring buffer

2018-07-25T14:29:41Z

Maintain the tracing on/off setting of the ring_buffer when switching to the trace buffer snapshot. Taking a snapshot is done by swapping the backup ring buffer (max_tr_buffer). But since the tracing on/off setting is defined by the ring buffer, when swapping it, the tracing on/off setting can also be changed. This causes a strange result like below: /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 0 > tracing_on /sys/kernel/debug/tracing # cat tracing_on 0 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 0 We don't touch tracing_on, but snapshot changes tracing_on setting each time. This is an anomaly, because user doesn't know that each "ring_buffer" stores its own tracing-enable state and the snapshot is done by swapping ring buffers. Link: http://lkml.kernel.org/r/153149929558.11274.11730609978254724394.stgit@devbox Cc: Ingo Molnar Cc: Shuah Khan Cc: Tom Zanussi Cc: Hiraku Toyooka Cc: stable@vger.kernel.org Fixes: debdd57f5145 ("tracing: Make a snapshot feature available from userspace") Signed-off-by: Masami Hiramatsu [ Updated commit log and comment in the code ] Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Fix a bunch of typos in comments

2018-06-04T21:28:19Z

An anonymous source sent me a bunch of typo fixes in the comments of ring_buffer.c file. That source did not want to be associated to this patch because they don't want to be known as "one of those" commiters (you know who you are!). They gave me permission to sign this off in my own name. Suggested-by: One-of-those-commiters@YouKnowWhoYouAre.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Add set/clear_current_oom_origin() during allocations

2018-04-06T12:56:52Z

As si_mem_available() can say there is enough memory even though the memory available is not useable by the ring buffer, it is best to not kill innocent applications because the ring buffer is taking up all the memory while it is trying to allocate a great deal of memory. If the allocator is user space (because kernel threads can also increase the size of the kernel ring buffer on boot up), then after si_mem_available() says there is enough memory, set the OOM killer to kill the current task if an OOM triggers during the allocation. Link: http://lkml.kernel.org/r/20180404062340.GD6312@dhcp22.suse.cz Suggested-by: Michal Hocko Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Check if memory is available before allocation

2018-04-06T12:56:52Z

The ring buffer is made up of a link list of pages. When making the ring buffer bigger, it will allocate all the pages it needs before adding to the ring buffer, and if it fails, it frees them and returns an error. This makes increasing the ring buffer size an all or nothing action. When this was first created, the pages were allocated with "NORETRY". This was to not cause any Out-Of-Memory (OOM) actions from allocating the ring buffer. But NORETRY was too strict, as the ring buffer would fail to expand even when there's memory available, but was taken up in the page cache. Commit 848618857d253 ("tracing/ring_buffer: Try harder to allocate") changed the allocating from NORETRY to RETRY_MAYFAIL. The RETRY_MAYFAIL would allocate from the page cache, but if there was no memory available, it would simple fail the allocation and not trigger an OOM. This worked fine, but had one problem. As the ring buffer would allocate one page at a time, it could take up all memory in the system before it failed to allocate and free that memory. If the allocation is happening and the ring buffer allocates all memory and then tries to take more than available, its allocation will not trigger an OOM, but if there's any allocation that happens someplace else, that could trigger an OOM, even though once the ring buffer's allocation fails, it would free up all the previous memory it tried to allocate, and allow other memory allocations to succeed. Commit d02bd27bd33dd ("mm/page_alloc.c: calculate 'available' memory in a separate function") separated out si_mem_availble() as a separate function that could be used to see how much memory is available in the system. Using this function to make sure that the ring buffer could be allocated before it tries to allocate pages we can avoid allocating all memory in the system and making it vulnerable to OOMs if other allocations are taking place. Link: http://lkml.kernel.org/r/1522320104-6573-1-git-send-email-zhaoyang.huang@spreadtrum.com CC: stable@vger.kernel.org Cc: linux-mm@kvack.org Fixes: 848618857d253 ("tracing/ring_buffer: Try harder to allocate") Requires: d02bd27bd33dd ("mm/page_alloc.c: calculate 'available' memory in a separate function") Reported-by: Zhaoyang Huang Tested-by: Joel Fernandes Signed-off-by: Steven Rostedt (VMware)

tracing: Mention trace_clock=global when warning about unstable clocks

2018-04-06T12:56:47Z

Mention the alternative of adding trace_clock=global to the kernel command line when we detect that we've used an unstable clock across a suspend/resume cycle. Link: http://lkml.kernel.org/r/20180330150132.16903-2-chris@chris-wilson.co.uk Signed-off-by: Chris Wilson Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Add nesting for adding events within events

2018-03-10T21:06:04Z

The ring-buffer code has recusion protection in case tracing ends up tracing itself, the ring-buffer will detect that it was called at the same context (normal, softirq, interrupt or NMI), and not continue to record the event. With the histogram synthetic events, they are called while tracing another event at the same context. The recusion protection triggers because it detects tracing at the same context and stops it. Add ring_buffer_nest_start() and ring_buffer_nest_end() that will notify the ring buffer that a trace is about to happen within another trace and that it is intended, and not to trigger the recursion blocking. Signed-off-by: Steven Rostedt (VMware)