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Luis Chamberlain 72647ea377 blktrace: break out of blktrace setup on concurrent calls
[ Upstream commit 1b0b283648163dae2a214ca28ed5a99f62a77319 ]

We use one blktrace per request_queue, that means one per the entire
disk.  So we cannot run one blktrace on say /dev/vda and then /dev/vda1,
or just two calls on /dev/vda.

We check for concurrent setup only at the very end of the blktrace setup though.

If we try to run two concurrent blktraces on the same block device the
second one will fail, and the first one seems to go on. However when
one tries to kill the first one one will see things like this:

The kernel will show these:

```
debugfs: File 'dropped' in directory 'nvme1n1' already present!
debugfs: File 'msg' in directory 'nvme1n1' already present!
debugfs: File 'trace0' in directory 'nvme1n1' already present!
``

And userspace just sees this error message for the second call:

```
blktrace /dev/nvme1n1
BLKTRACESETUP(2) /dev/nvme1n1 failed: 5/Input/output error
```

The first userspace process #1 will also claim that the files
were taken underneath their nose as well. The files are taken
away form the first process given that when the second blktrace
fails, it will follow up with a BLKTRACESTOP and BLKTRACETEARDOWN.
This means that even if go-happy process #1 is waiting for blktrace
data, we *have* been asked to take teardown the blktrace.

This can easily be reproduced with break-blktrace [0] run_0005.sh test.

Just break out early if we know we're already going to fail, this will
prevent trying to create the files all over again, which we know still
exist.

[0] https://github.com/mcgrof/break-blktrace

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-06-30 15:37:05 -04:00
arch arm64: sve: Fix build failure when ARM64_SVE=y and SYSCTL=n 2020-06-30 15:37:05 -04:00
block block/bio-integrity: don't free 'buf' if bio_integrity_add_page() failed 2020-06-30 15:36:43 -04:00
certs
crypto crypto: algboss - don't wait during notifier callback 2020-06-24 17:50:51 +02:00
Documentation dt-bindings: display: mediatek: control dpi pins mode to avoid leakage 2020-06-22 09:30:58 +02:00
drivers pinctrl: tegra: Use noirq suspend/resume callbacks 2020-06-30 15:37:04 -04:00
fs afs: Fix storage of cell names 2020-06-30 15:37:02 -04:00
include net: qed: fix left elements count calculation 2020-06-30 15:36:58 -04:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel blktrace: break out of blktrace setup on concurrent calls 2020-06-30 15:37:05 -04:00
lib test_objagg: Fix potential memory leak in error handling 2020-06-30 15:37:04 -04:00
LICENSES
mm mm: call cond_resched() from deferred_init_memmap() 2020-06-22 09:31:14 +02:00
net netfilter: ipset: fix unaligned atomic access 2020-06-30 15:37:01 -04:00
samples bpf, xdp, samples: Fix null pointer dereference in *_user code 2020-06-30 15:36:55 -04:00
scripts recordmcount: support >64k sections 2020-06-30 15:37:05 -04:00
security selinux: fix double free 2020-06-24 17:50:48 +02:00
sound ASoC: rockchip: Fix a reference count leak. 2020-06-30 15:36:57 -04:00
tools selftests/net: report etf errors correctly 2020-06-30 15:36:58 -04:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm64: Save the host's PtrAuth keys in non-preemptible context 2020-06-17 16:40:38 +02:00
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Makefile Linux 5.4.49 2020-06-24 17:50:53 +02:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.