This should actually be on it's way to Linus for .35, shouldn't it? On Thu, Jun 24, 2010 at 01:02:14PM +1000, npiggin@xxxxxxx wrote: > list_for_each_entry_safe is not suitable to protect against concurrent > modification of the list. 6754af6 introduced a race in sb walking. > > list_for_each_entry can use the trick of pinning the current entry in > the list before we drop and retake the lock because it subsequently > follows cur->next. However list_for_each_entry_safe saves n=cur->next > for following before entering the loop body, so when the lock is > dropped, n may be deleted. > > Signed-off-by: Nick Piggin <npiggin@xxxxxxx> > --- > fs/dcache.c | 2 ++ > fs/super.c | 6 ++++++ > include/linux/list.h | 15 +++++++++++++++ > 3 files changed, 23 insertions(+) > > Index: linux-2.6/fs/dcache.c > =================================================================== > --- linux-2.6.orig/fs/dcache.c > +++ linux-2.6/fs/dcache.c > @@ -590,6 +590,8 @@ static void prune_dcache(int count) > up_read(&sb->s_umount); > } > spin_lock(&sb_lock); > + /* lock was dropped, must reset next */ > + list_safe_reset_next(sb, n, s_list); > count -= pruned; > __put_super(sb); > /* more work left to do? */ > Index: linux-2.6/fs/super.c > =================================================================== > --- linux-2.6.orig/fs/super.c > +++ linux-2.6/fs/super.c > @@ -374,6 +374,8 @@ void sync_supers(void) > up_read(&sb->s_umount); > > spin_lock(&sb_lock); > + /* lock was dropped, must reset next */ > + list_safe_reset_next(sb, n, s_list); > __put_super(sb); > } > } > @@ -405,6 +407,8 @@ void iterate_supers(void (*f)(struct sup > up_read(&sb->s_umount); > > spin_lock(&sb_lock); > + /* lock was dropped, must reset next */ > + list_safe_reset_next(sb, n, s_list); > __put_super(sb); > } > spin_unlock(&sb_lock); > @@ -585,6 +589,8 @@ static void do_emergency_remount(struct > } > up_write(&sb->s_umount); > spin_lock(&sb_lock); > + /* lock was dropped, must reset next */ > + list_safe_reset_next(sb, n, s_list); > __put_super(sb); > } > spin_unlock(&sb_lock); > Index: linux-2.6/include/linux/list.h > =================================================================== > --- linux-2.6.orig/include/linux/list.h > +++ linux-2.6/include/linux/list.h > @@ -544,6 +544,21 @@ static inline void list_splice_tail_init > &pos->member != (head); \ > pos = n, n = list_entry(n->member.prev, typeof(*n), member)) > > +/** > + * list_safe_reset_next - reset a stale list_for_each_entry_safe loop > + * @pos: the loop cursor used in the list_for_each_entry_safe loop > + * @n: temporary storage used in list_for_each_entry_safe > + * @member: the name of the list_struct within the struct. > + * > + * list_safe_reset_next is not safe to use in general if the list may be > + * modified concurrently (eg. the lock is dropped in the loop body). An > + * exception to this is if the cursor element (pos) is pinned in the list, > + * and list_safe_reset_next is called after re-taking the lock and before > + * completing the current iteration of the loop body. > + */ > +#define list_safe_reset_next(pos, n, member) \ > + n = list_entry(pos->member.next, typeof(*pos), member) > + > /* > * Double linked lists with a single pointer list head. > * Mostly useful for hash tables where the two pointer list head is > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html ---end quoted text--- -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
