From: Eric Dumazet Date: Sat, 25 Mar 2006 11:08:00 +0000 (-0800) Subject: [PATCH] No need to protect current->group_info in sys_getgroups(), in_group_p() and... X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=231bed205879236357171e50bd8965e70797ecdc;p=GitHub%2Fmt8127%2Fandroid_kernel_alcatel_ttab.git [PATCH] No need to protect current->group_info in sys_getgroups(), in_group_p() and in_egroup_p() While doing some benchmarks of an Apache/PHP SMP server, I noticed high oprofile numbers in in_group_p() and _atomic_dec_and_lock(). rank percent 1 4.8911 % __link_path_walk 2 4.8503 % __d_lookup *3 4.2911 % _atomic_dec_and_lock 4 3.9307 % __copy_to_user_ll 5 4.9004 % sysenter_past_esp *6 3.3248 % in_group_p It appears that in_group_p() does an uncessary get_group_info(current->group_info); /* atomic_inc() */ ... /* access current->group_info */ put_group_info(current->group_info); /* _atomic_dec_and_lock */ It is not necessary to do this, because the current task holds a reference on its own group_info, and this reference cannot change during the lookup. This patch deletes the get_group_info()/put_group_info() pair from sys_getgroups(), in_group_p() and in_egroup_p() functions. Signed-off-by: Eric Dumazet Cc: Tim Hockin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/sys.c b/kernel/sys.c index 421009cedb51..119fb0d9e24e 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1421,7 +1421,6 @@ asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist) return -EINVAL; /* no need to grab task_lock here; it cannot change */ - get_group_info(current->group_info); i = current->group_info->ngroups; if (gidsetsize) { if (i > gidsetsize) { @@ -1434,7 +1433,6 @@ asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist) } } out: - put_group_info(current->group_info); return i; } @@ -1475,9 +1473,7 @@ int in_group_p(gid_t grp) { int retval = 1; if (grp != current->fsgid) { - get_group_info(current->group_info); retval = groups_search(current->group_info, grp); - put_group_info(current->group_info); } return retval; } @@ -1488,9 +1484,7 @@ int in_egroup_p(gid_t grp) { int retval = 1; if (grp != current->egid) { - get_group_info(current->group_info); retval = groups_search(current->group_info, grp); - put_group_info(current->group_info); } return retval; }