Messages in this thread Patch in this message | | | From | Andi Kleen <> | Subject | [PATCH] [3/9] SYSCTL: Add proc_rcu_string to manage sysctls using rcu strings | Date | Tue, 5 Jan 2010 03:15:28 +0100 (CET) |
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Add a helper to use the new rcu strings for managing access to text sysctls. Conversions will be in follow-on patches.
An alternative would be to use seqlocks here, but RCU seemed cleaner.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
--- include/linux/sysctl.h | 2 + kernel/sysctl.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++ kernel/sysctl_check.c | 1 3 files changed, 69 insertions(+)
Index: linux-2.6.33-rc2-ak/include/linux/sysctl.h =================================================================== --- linux-2.6.33-rc2-ak.orig/include/linux/sysctl.h +++ linux-2.6.33-rc2-ak/include/linux/sysctl.h @@ -969,6 +969,8 @@ typedef int proc_handler (struct ctl_tab extern int proc_dostring(struct ctl_table *, int, void __user *, size_t *, loff_t *); +extern int proc_rcu_string(struct ctl_table *, int, + void __user *, size_t *, loff_t *); extern int proc_dointvec(struct ctl_table *, int, void __user *, size_t *, loff_t *); extern int proc_dointvec_minmax(struct ctl_table *, int, Index: linux-2.6.33-rc2-ak/kernel/sysctl.c =================================================================== --- linux-2.6.33-rc2-ak.orig/kernel/sysctl.c +++ linux-2.6.33-rc2-ak/kernel/sysctl.c @@ -50,6 +50,7 @@ #include <linux/ftrace.h> #include <linux/slow-work.h> #include <linux/perf_event.h> +#include <linux/rcustring.h> #include <asm/uaccess.h> #include <asm/processor.h> @@ -2016,6 +2017,60 @@ static int _proc_do_string(void* data, i } /** + * proc_rcu_string - sysctl string with rcu protection + * @table: the sysctl table + * @write: %TRUE if this is a write to the sysctl file + * @buffer: the user buffer + * @lenp: the size of the user buffer + * @ppos: file position + * + * Handle a string sysctl similar to proc_dostring. + * The main difference is that the data pointer in the table + * points to a pointer to a string. The string should be initially + * pointing to a statically allocated (as a C object, not on the heap) + * default. When it is replaced old uses will be protected by + * RCU. The reader should use rcu_read_lock()/unlock() or + * access_rcu_string(). + */ +int proc_rcu_string(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int ret; + + if (write) { + /* protect writers against each other */ + static DEFINE_MUTEX(rcu_string_mutex); + char *old; + char *new; + + new = alloc_rcu_string(table->maxlen, GFP_KERNEL); + if (!new) + return -ENOMEM; + mutex_lock(&rcu_string_mutex); + old = *(char **)(table->data); + strcpy(new, old); + ret = _proc_do_string(new, table->maxlen, write, buffer, lenp, ppos); + rcu_assign_pointer(*(char **)(table->data), new); + /* + * For the first initialization allow constant strings. + */ + if (!kernel_address((unsigned long)old)) + free_rcu_string(old); + mutex_unlock(&rcu_string_mutex); + } else { + char *str; + + str = access_rcu_string((char **)(table->data), table->maxlen, + GFP_KERNEL); + if (!str) + return -ENOMEM; + ret = _proc_do_string(str, table->maxlen, write, buffer, lenp, ppos); + kfree(str); + } + return ret; +} + +/** * proc_dostring - read a string sysctl * @table: the sysctl table * @write: %TRUE if this is a write to the sysctl file @@ -2030,6 +2085,10 @@ static int _proc_do_string(void* data, i * and a newline '\n' is added. It is truncated if the buffer is * not large enough. * + * WARNING: this should be only used for read only strings + * or when you have a wrapper with special locking. Otherwise + * use proc_rcu_string to avoid races with the consumer. + * * Returns 0 on success. */ int proc_dostring(struct ctl_table *table, int write, @@ -2614,6 +2673,12 @@ int proc_dostring(struct ctl_table *tabl return -ENOSYS; } +int proc_rcu_string(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + return -ENOSYS; +} + int proc_dointvec(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { @@ -2670,6 +2735,7 @@ EXPORT_SYMBOL(proc_dointvec_minmax); EXPORT_SYMBOL(proc_dointvec_userhz_jiffies); EXPORT_SYMBOL(proc_dointvec_ms_jiffies); EXPORT_SYMBOL(proc_dostring); +EXPORT_SYMBOL(proc_rcu_string); EXPORT_SYMBOL(proc_doulongvec_minmax); EXPORT_SYMBOL(proc_doulongvec_ms_jiffies_minmax); EXPORT_SYMBOL(register_sysctl_table); Index: linux-2.6.33-rc2-ak/kernel/sysctl_check.c =================================================================== --- linux-2.6.33-rc2-ak.orig/kernel/sysctl_check.c +++ linux-2.6.33-rc2-ak/kernel/sysctl_check.c @@ -131,6 +131,7 @@ int sysctl_check_table(struct nsproxy *n set_fail(&fail, table, "Directory with extra2"); } else { if ((table->proc_handler == proc_dostring) || + (table->proc_handler == proc_rcu_string) || (table->proc_handler == proc_dointvec) || (table->proc_handler == proc_dointvec_minmax) || (table->proc_handler == proc_dointvec_jiffies) ||
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