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12c1dc8e74
The mems_allowed field can be modified by other tasks, so it isn't safe to
access it with alloc_lock unlocked even in the current process context.
Say there are two tasks: A from cpusetA is performing set_mempolicy(2),
and B is changing cpusetA's cpuset.mems:
A (set_mempolicy) B (echo xx > cpuset.mems)
-------------------------------------------------------
pol = mpol_new();
update_tasks_nodemask(cpusetA) {
foreach t in cpusetA {
cpuset_change_task_nodemask(t) {
mpol_set_nodemask(pol) {
task_lock(t); // t could be A
new = f(A->mems_allowed);
update t->mems_allowed;
pol.create(pol, new);
task_unlock(t);
}
}
}
}
task_lock(A);
A->mempolicy = pol;
task_unlock(A);
In this case A's pol->nodes is computed by old mems_allowed, and could
be inconsistent with A's new mems_allowed.
While it is different when replacing vmas' policy: the pol->nodes is
gone wild only when current_cpuset_is_being_rebound():
A (mbind) B (echo xx > cpuset.mems)
-------------------------------------------------------
pol = mpol_new();
mmap_write_lock(A->mm);
cpuset_being_rebound = cpusetA;
update_tasks_nodemask(cpusetA) {
foreach t in cpusetA {
cpuset_change_task_nodemask(t) {
mpol_set_nodemask(pol) {
task_lock(t); // t could be A
mask = f(A->mems_allowed);
update t->mems_allowed;
pol.create(pol, mask);
task_unlock(t);
}
}
foreach v in A->mm {
if (cpuset_being_rebound == cpusetA)
pol.rebind(pol, cpuset.mems);
v->vma_policy = pol;
}
mmap_write_unlock(A->mm);
mmap_write_lock(t->mm);
mpol_rebind_mm(t->mm);
mmap_write_unlock(t->mm);
}
}
cpuset_being_rebound = NULL;
In this case, the cpuset.mems, which has already done updating, is finally
used for calculating pol->nodes, rather than A->mems_allowed. So it is OK
to call mpol_set_nodemask() with alloc_lock unlocked when doing mbind(2).
Link: https://lkml.kernel.org/r/20220811124157.74888-1-wuyun.abel@bytedance.com
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.