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prb_next_seq() always iterates from the first known sequence number.
In the worst case, it might loop 8k times for 256kB buffer,
15k times for 512kB buffer, and 64k times for 2MB buffer.
It was reported that polling and reading using syslog interface
might occupy 50% of CPU.
Speedup the search by storing @id of the last finalized descriptor.
The loop is still needed because the @id is stored and read in the best
effort way. An atomic variable is used to keep the @id consistent.
But the stores and reads are not serialized against each other.
The descriptor could get reused in the meantime. The related sequence
number will be used only when it is still valid.
An invalid value should be read _only_ when there is a flood of messages
and the ringbuffer is rapidly reused. The performance is the least
problem in this case.
Reported-by: Chunlei Wang <chunlei.wang@mediatek.com>
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/1642770388-17327-1-git-send-email-quic_mojha@quicinc.com
Link: https://lore.kernel.org/lkml/YXlddJxLh77DKfIO@alley/T/#m43062e8b2a17f8dbc8c6ccdb8851fb0dbaabbb14
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The command 'find ./kernel/printk/ | xargs ./scripts/kernel-doc -none'
reported a mismatch with the kernel-doc of prb_rec_init_wr().
Rectify the kernel-doc, such that no issues remain for ./kernel/printk/.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210125081748.19903-1-lukas.bulwahn@gmail.com
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If a reader provides a buffer that is smaller than the message text,
the @text_len field of @info will have a value larger than the buffer
size. If readers blindly read @text_len bytes of data without
checking the size, they will read beyond their buffer.
Add this check to record_print_text() to properly recognize when such
truncation has occurred.
Add a maximum size argument to the ringbuffer function to extend
records so that records can not be created that are larger than the
buffer size of readers.
When extending records (LOG_CONT), do not extend records beyond
LOG_LINE_MAX since that is the maximum size available in the buffers
used by consoles and syslog.
Fixes: f5f022e53b87 ("printk: reimplement log_cont using record extension")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200930090134.8723-2-john.ogness@linutronix.de
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Since there is no code that will ever store anything into the dict
ring, remove it. If any future dictionary properties are to be
added, these should be added to the struct printk_info.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200918223421.21621-4-john.ogness@linutronix.de
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Dictionaries are only used for SUBSYSTEM and DEVICE properties. The
current implementation stores the property names each time they are
used. This requires more space than otherwise necessary. Also,
because the dictionary entries are currently considered optional,
it cannot be relied upon that they are always available, even if the
writer wanted to store them. These issues will increase should new
dictionary properties be introduced.
Rather than storing the subsystem and device properties in the
dict ring, introduce a struct dev_printk_info with separate fields
to store only the property values. Embed this struct within the
struct printk_info to provide guaranteed availability.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87mu1jl6ne.fsf@jogness.linutronix.de
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The majority of the size of a descriptor is taken up by meta data,
which is often not of interest to the ringbuffer (for example,
when performing state checks). Since descriptors are often
temporarily stored on the stack, keeping their size minimal will
help reduce stack pressure.
Rather than embedding the printk_info into the descriptor, create
a separate printk_info array. The index of a descriptor in the
descriptor array corresponds to the printk_info with the same
index in the printk_info array. The rules for validity of a
printk_info match the existing rules for the data blocks: the
descriptor must be in a consistent state.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200918223421.21621-2-john.ogness@linutronix.de
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Add support for extending the newest data block. For this, introduce
a new finalization state (desc_finalized) denoting a committed
descriptor that cannot be extended.
Until a record is finalized, a writer can reopen that record to
append new data. Reopening a record means transitioning from the
desc_committed state back to the desc_reserved state.
A writer can explicitly finalize a record if there is no intention
of extending it. Also, records are automatically finalized when a
new record is reserved. This relieves writers of needing to
explicitly finalize while also making such records available to
readers sooner. (Readers can only traverse finalized records.)
Four new memory barrier pairs are introduced. Two of them are
insignificant additions (data_realloc:A/desc_read:D and
data_realloc:A/data_push_tail:B) because they are alternate path
memory barriers that exactly match the purpose, pairing, and
context of the two existing memory barrier pairs they provide an
alternate path for. The other two new memory barrier pairs are
significant additions:
desc_reopen_last:A / _prb_commit:B - When reopening a descriptor,
ensure the state transitions back to desc_reserved before
fully trusting the descriptor data.
_prb_commit:B / desc_reserve:D - When committing a descriptor,
ensure the state transitions to desc_committed before checking
the head ID to see if the descriptor needs to be finalized.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-6-john.ogness@linutronix.de
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Rather than deriving the state by evaluating bits within the flags
area of the state variable, assign the states explicit values and
set those values in the flags area. Introduce macros to make it
simple to read and write state values for the state variable.
Although the functionality is preserved, the binary representation
for the states is changed.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-5-john.ogness@linutronix.de
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With commit 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer"),
printk() started silently dropping messages without text because such
records are not supported by the new printk ringbuffer.
Add support for such records.
Currently dataless records are denoted by INVALID_LPOS in order
to recognize failed prb_reserve() calls. Change the ringbuffer
to instead use two different identifiers (FAILED_LPOS and
NO_LPOS) to distinguish between failed prb_reserve() records and
successful dataless records, respectively.
Fixes: 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer")
Fixes: https://lkml.kernel.org/r/20200718121053.GA691245@elver.google.com
Reported-by: Marco Elver <elver@google.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200721132528.9661-1-john.ogness@linutronix.de
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Introduce a multi-reader multi-writer lockless ringbuffer for storing
the kernel log messages. Readers and writers may use their API from
any context (including scheduler and NMI). This ringbuffer will make
it possible to decouple printk() callers from any context, locking,
or console constraints. It also makes it possible for readers to have
full access to the ringbuffer contents at any time and context (for
example from any panic situation).
The printk_ringbuffer is made up of 3 internal ringbuffers:
desc_ring:
A ring of descriptors. A descriptor contains all record meta data
(sequence number, timestamp, loglevel, etc.) as well as internal state
information about the record and logical positions specifying where in
the other ringbuffers the text and dictionary strings are located.
text_data_ring:
A ring of data blocks. A data block consists of an unsigned long
integer (ID) that maps to a desc_ring index followed by the text
string of the record.
dict_data_ring:
A ring of data blocks. A data block consists of an unsigned long
integer (ID) that maps to a desc_ring index followed by the dictionary
string of the record.
The internal state information of a descriptor is the key element to
allow readers and writers to locklessly synchronize access to the data.
Co-developed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200709132344.760-3-john.ogness@linutronix.de
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