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Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull two cgroup fixes from Tejun Heo: "This containes two patches fixing a refcnt race bug during css_put(). Decrementing and checking the value weren't atomic and two tasks could think that they both pushed the counter to zero." * 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: cgroups: Account for CSS_DEACT_BIAS in __css_put cgroup: make sure that decisions in __css_put are atomic
This commit is contained in:
commit
2ce5682947
1 changed files with 10 additions and 3 deletions
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@ -255,12 +255,17 @@ int cgroup_lock_is_held(void)
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EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
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EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
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static int css_unbias_refcnt(int refcnt)
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{
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return refcnt >= 0 ? refcnt : refcnt - CSS_DEACT_BIAS;
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}
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/* the current nr of refs, always >= 0 whether @css is deactivated or not */
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/* the current nr of refs, always >= 0 whether @css is deactivated or not */
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static int css_refcnt(struct cgroup_subsys_state *css)
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static int css_refcnt(struct cgroup_subsys_state *css)
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{
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{
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int v = atomic_read(&css->refcnt);
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int v = atomic_read(&css->refcnt);
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return v >= 0 ? v : v - CSS_DEACT_BIAS;
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return css_unbias_refcnt(v);
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}
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}
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/* convenient tests for these bits */
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/* convenient tests for these bits */
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@ -4982,10 +4987,12 @@ EXPORT_SYMBOL_GPL(__css_tryget);
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void __css_put(struct cgroup_subsys_state *css)
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void __css_put(struct cgroup_subsys_state *css)
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{
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{
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struct cgroup *cgrp = css->cgroup;
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struct cgroup *cgrp = css->cgroup;
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int v;
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rcu_read_lock();
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rcu_read_lock();
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atomic_dec(&css->refcnt);
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v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));
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switch (css_refcnt(css)) {
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switch (v) {
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case 1:
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case 1:
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if (notify_on_release(cgrp)) {
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if (notify_on_release(cgrp)) {
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set_bit(CGRP_RELEASABLE, &cgrp->flags);
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set_bit(CGRP_RELEASABLE, &cgrp->flags);
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