Messages in this thread | | | Date | Tue, 24 Jun 2008 10:56:34 -0500 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH 3/8] CGroup Files: Move the release_agent file to use typed handlers |
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Quoting menage@google.com (menage@google.com): > Adds cgroup_release_agent_write() and cgroup_release_agent_show() > methods to handle writing/reading the path to a cgroup hierarchy's > release agent. As a result, cgroup_common_file_read() is now unnecessary. > > As part of the change, a previously-tolerated race in > cgroup_release_agent() is avoided by copying the current > release_agent_path prior to calling call_usermode_helper(). > > Signed-off-by: Paul Menage <menage@google.com> > > --- > include/linux/cgroup.h | 2 > kernel/cgroup.c | 125 ++++++++++++++++++++++--------------------------- > 2 files changed, 59 insertions(+), 68 deletions(-) > > Index: cws-2.6.26-rc5-mm3/kernel/cgroup.c > =================================================================== > --- cws-2.6.26-rc5-mm3.orig/kernel/cgroup.c > +++ cws-2.6.26-rc5-mm3/kernel/cgroup.c > @@ -89,11 +89,7 @@ struct cgroupfs_root { > /* Hierarchy-specific flags */ > unsigned long flags; > > - /* The path to use for release notifications. No locking > - * between setting and use - so if userspace updates this > - * while child cgroups exist, you could miss a > - * notification. We ensure that it's always a valid > - * NUL-terminated string */ > + /* The path to use for release notifications. */ > char release_agent_path[PATH_MAX]; > }; > > @@ -1329,6 +1325,45 @@ enum cgroup_filetype { > FILE_RELEASE_AGENT, > }; > > +/** > + * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive. > + * @cgrp: the cgroup to be checked for liveness > + * > + * Returns true (with lock held) on success, or false (with no lock > + * held) on failure. > + */ > +int cgroup_lock_live_group(struct cgroup *cgrp)
Would seem more consistent to call the return type bool, but otherwise this patch looks good.
Acked-by: Serge Hallyn <serue@us.ibm.com>
thanks, -serge
> +{ > + mutex_lock(&cgroup_mutex); > + if (cgroup_is_removed(cgrp)) { > + mutex_unlock(&cgroup_mutex); > + return false; > + } > + return true; > +} > + > +static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft, > + const char *buffer) > +{ > + BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX); > + if (!cgroup_lock_live_group(cgrp)) > + return -ENODEV; > + strcpy(cgrp->root->release_agent_path, buffer); > + mutex_unlock(&cgroup_mutex); > + return 0; > +} > + > +static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft, > + struct seq_file *seq) > +{ > + if (!cgroup_lock_live_group(cgrp)) > + return -ENODEV; > + seq_puts(seq, cgrp->root->release_agent_path); > + seq_putc(seq, '\n'); > + mutex_unlock(&cgroup_mutex); > + return 0; > +} > + > static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft, > struct file *file, > const char __user *userbuf, > @@ -1443,10 +1478,6 @@ static ssize_t cgroup_common_file_write( > else > clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); > break; > - case FILE_RELEASE_AGENT: > - BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX); > - strcpy(cgrp->root->release_agent_path, buffer); > - break; > default: > retval = -EINVAL; > goto out2; > @@ -1506,49 +1537,6 @@ static ssize_t cgroup_read_s64(struct cg > return simple_read_from_buffer(buf, nbytes, ppos, tmp, len); > } > > -static ssize_t cgroup_common_file_read(struct cgroup *cgrp, > - struct cftype *cft, > - struct file *file, > - char __user *buf, > - size_t nbytes, loff_t *ppos) > -{ > - enum cgroup_filetype type = cft->private; > - char *page; > - ssize_t retval = 0; > - char *s; > - > - if (!(page = (char *)__get_free_page(GFP_KERNEL))) > - return -ENOMEM; > - > - s = page; > - > - switch (type) { > - case FILE_RELEASE_AGENT: > - { > - struct cgroupfs_root *root; > - size_t n; > - mutex_lock(&cgroup_mutex); > - root = cgrp->root; > - n = strnlen(root->release_agent_path, > - sizeof(root->release_agent_path)); > - n = min(n, (size_t) PAGE_SIZE); > - strncpy(s, root->release_agent_path, n); > - mutex_unlock(&cgroup_mutex); > - s += n; > - break; > - } > - default: > - retval = -EINVAL; > - goto out; > - } > - *s++ = '\n'; > - > - retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page); > -out: > - free_page((unsigned long)page); > - return retval; > -} > - > static ssize_t cgroup_file_read(struct file *file, char __user *buf, > size_t nbytes, loff_t *ppos) > { > @@ -1606,6 +1594,7 @@ static int cgroup_seqfile_release(struct > > static struct file_operations cgroup_seqfile_operations = { > .read = seq_read, > + .write = cgroup_file_write, > .llseek = seq_lseek, > .release = cgroup_seqfile_release, > }; > @@ -2283,8 +2272,9 @@ static struct cftype files[] = { > > static struct cftype cft_release_agent = { > .name = "release_agent", > - .read = cgroup_common_file_read, > - .write = cgroup_common_file_write, > + .read_seq_string = cgroup_release_agent_show, > + .write_string = cgroup_release_agent_write, > + .max_write_len = PATH_MAX, > .private = FILE_RELEASE_AGENT, > }; > > @@ -3113,27 +3103,24 @@ static void cgroup_release_agent(struct > while (!list_empty(&release_list)) { > char *argv[3], *envp[3]; > int i; > - char *pathbuf; > + char *pathbuf = NULL, *agentbuf = NULL; > struct cgroup *cgrp = list_entry(release_list.next, > struct cgroup, > release_list); > list_del_init(&cgrp->release_list); > spin_unlock(&release_list_lock); > pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); > - if (!pathbuf) { > - spin_lock(&release_list_lock); > - continue; > - } > - > - if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) { > - kfree(pathbuf); > - spin_lock(&release_list_lock); > - continue; > - } > + if (!pathbuf) > + goto continue_free; > + if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) > + goto continue_free; > + agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL); > + if (!agentbuf) > + goto continue_free; > > i = 0; > - argv[i++] = cgrp->root->release_agent_path; > - argv[i++] = (char *)pathbuf; > + argv[i++] = agentbuf; > + argv[i++] = pathbuf; > argv[i] = NULL; > > i = 0; > @@ -3147,8 +3134,10 @@ static void cgroup_release_agent(struct > * be a slow process */ > mutex_unlock(&cgroup_mutex); > call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC); > - kfree(pathbuf); > mutex_lock(&cgroup_mutex); > + continue_free: > + kfree(pathbuf); > + kfree(agentbuf); > spin_lock(&release_list_lock); > } > spin_unlock(&release_list_lock); > Index: cws-2.6.26-rc5-mm3/include/linux/cgroup.h > =================================================================== > --- cws-2.6.26-rc5-mm3.orig/include/linux/cgroup.h > +++ cws-2.6.26-rc5-mm3/include/linux/cgroup.h > @@ -295,6 +295,8 @@ int cgroup_add_files(struct cgroup *cgrp > > int cgroup_is_removed(const struct cgroup *cgrp); > > +int cgroup_lock_live_group(struct cgroup *cgrp); > + > int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen); > > int cgroup_task_count(const struct cgroup *cgrp); > > --
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