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Currently get_perf_callchain only supports user stack walking for
the current task. Passing the correct *crosstask* param will return
0 frames if the task passed to __bpf_get_stack isn't the current
one instead of a single incorrect frame/address. This change
passes the correct *crosstask* param but also does a preemptive
check in __bpf_get_stack if the task is current and returns
-EOPNOTSUPP if it is not.
This issue was found using bpf_get_task_stack inside a BPF
iterator ("iter/task"), which iterates over all tasks.
bpf_get_task_stack works fine for fetching kernel stacks
but because get_perf_callchain relies on the caller to know
if the requested *task* is the current one (via *crosstask*)
it was failing in a confusing way.
It might be possible to get user stacks for all tasks utilizing
something like access_process_vm but that requires the bpf
program calling bpf_get_task_stack to be sleepable and would
therefore be a breaking change.
Fixes:
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.. | ||
accounting | ||
arch | ||
bootconfig | ||
bpf | ||
build | ||
certs | ||
cgroup | ||
counter | ||
crypto/ccp | ||
debugging | ||
edid | ||
firewire | ||
firmware | ||
gpio | ||
hv | ||
iio | ||
include | ||
kvm/kvm_stat | ||
laptop | ||
leds | ||
lib | ||
memory-model | ||
mm | ||
net/ynl | ||
objtool | ||
pci | ||
pcmcia | ||
perf | ||
power | ||
rcu | ||
scripts | ||
spi | ||
testing | ||
thermal | ||
time | ||
tracing | ||
usb | ||
verification | ||
virtio | ||
wmi | ||
workqueue | ||
Makefile |