Messages in this thread Patch in this message | | | Date | Fri, 2 Jun 2006 13:43:46 -0700 | From | Andrew Morton <> | Subject | Re: lock_kernel called under spinlock in NFS |
| |
Trond Myklebust <Trond.Myklebust@netapp.com> wrote: > > On Fri, 2006-06-02 at 16:24 -0400, Joe Korty wrote: > > On Thu, Jun 01, 2006 at 04:13:39PM -0400, Trond Myklebust wrote: > > > On Thu, 2006-06-01 at 15:55 -0400, Joe Korty wrote: > > >> Tree 5fdccf2354269702f71beb8e0a2942e4167fd992 > > >> > > >> [PATCH] vfs: *at functions: core > > >> > > >> introduced a bug where lock_kernel() can be called from > > >> under a spinlock. To trigger the bug one must have > > >> CONFIG_PREEMPT_BKL=y and be using NFS heavily. It is > > >> somewhat rare and, so far, haven't traced down the userland > > >> sequence that causes the fatal path to be taken. > > >> > > >> The bug was caused by the insertion into do_path_lookup() > > >> of a call to file_permission(). do_path_lookup() > > >> read-locks current->fs->lock for most of its operation. > > >> file_permission() calls permission() which calls > > >> nfs_permission(), which has one path through it > > >> that uses lock_kernel(). > > > > > Nowhere should anyone be calling file_permission() under a spinlock. > > > > > > Why would you need to read-protect current->fs in the case where you are > > > starting from a file? The correct thing to do there would appear to be > > > to read_protect only the cases where (*name=='/') and (dfd == AT_FDCWD). > > > > > > Something like the attached patch... > > > > > > Hi Trond, > > I've been running with the patch for the last few hours, on an nfs-rooted > > system, and it has been working fine. Any plans to submit this for 2.6.17? > > It probably ought to be, given the nature of the sin. Andrew? >
OK.
Just to confirm, this is final?
From: Trond Myklebust <Trond.Myklebust@netapp.com>
We're presently running lock_kernel() under fs_lock via nfs's ->permission handler. That's a ranking bug and sometimes a sleep-in-spinlock bug. This problem was introduced in the openat() patchset.
We should not need to hold the current->fs->lock for a codepath that doesn't use current->fs.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: Al Viro <viro@ftp.linux.org.uk> Signed-off-by: Andrew Morton <akpm@osdl.org> ---
fs/namei.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-)
diff -puN fs/namei.c~fs-nameic-call-to-file_permission-under-a-spinlock-in-do_lookup_path fs/namei.c --- 25/fs/namei.c~fs-nameic-call-to-file_permission-under-a-spinlock-in-do_lookup_path Fri Jun 2 13:39:52 2006 +++ 25-akpm/fs/namei.c Fri Jun 2 13:39:52 2006 @@ -1080,8 +1080,8 @@ static int fastcall do_path_lookup(int d nd->flags = flags; nd->depth = 0; - read_lock(¤t->fs->lock); if (*name=='/') { + read_lock(¤t->fs->lock); if (current->fs->altroot && !(nd->flags & LOOKUP_NOALT)) { nd->mnt = mntget(current->fs->altrootmnt); nd->dentry = dget(current->fs->altroot); @@ -1092,9 +1092,12 @@ static int fastcall do_path_lookup(int d } nd->mnt = mntget(current->fs->rootmnt); nd->dentry = dget(current->fs->root); + read_unlock(¤t->fs->lock); } else if (dfd == AT_FDCWD) { + read_lock(¤t->fs->lock); nd->mnt = mntget(current->fs->pwdmnt); nd->dentry = dget(current->fs->pwd); + read_unlock(¤t->fs->lock); } else { struct dentry *dentry; @@ -1118,7 +1121,6 @@ static int fastcall do_path_lookup(int d fput_light(file, fput_needed); } - read_unlock(¤t->fs->lock); current->total_link_count = 0; retval = link_path_walk(name, nd); out: _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |