Vladimir Davydov <[email protected]> writes: > From: Al Viro <[email protected]> > > Backport mainstream commit: > > commit fe91522a7ba82ca1a51b07e19954b3825e4aaa22 > Author: Al Viro <[email protected]> > Date: Sat May 3 00:02:25 2014 -0400 > > don't remove from shrink list in select_collect() > > If we find something already on a shrink list, just increment > data->found and do nothing else. Loops in shrink_dcache_parent() and > check_submounts_and_drop() will do the right thing - everything we > did put into our list will be evicted and if there had been nothing, > but data->found got non-zero, well, we have somebody else shrinking > those guys; just try again. > > Signed-off-by: Al Viro <[email protected]> > > Dcache shrinker temporarily adds dentries to a shrink list before > dropping them. This list is allocated on stack and not protected by any > locks, therefore only the caller (i.e. the process scanning dcache) can > safely remove entries from it. Currently, however, dentries can be > removed from a shrink list by dentry_kill() and select_collect(). If > this races with a shrinker invocation, we'll get list corruption: > > WARNING: at lib/list_debug.c:59 __list_del_entry+0xa1/0xd0() > list_del corruption. prev->next should be ffff8801e1621980, but was > ffff8801de3155c0 > CPU: 5 PID: 58031 Comm: trinity-main ve: 101 Not tainted > 3.10.0-327.3.1.vz7.10.11 #1 10.11 > 000000000000003b 00000000d7f09cf1 ffff8800a3ca3b80 ffffffff816306f3 > ffff8800a3ca3bb8 ffffffff8107b4c0 ffff8801e1621900 ffff8801e1621980 > ffff880207c172b8 ffff8801e27069c0 0000000000000000 ffff8800a3ca3c20 > Call Trace: > [<ffffffff816306f3>] dump_stack+0x19/0x1b > [<ffffffff8107b4c0>] warn_slowpath_common+0x70/0xb0 > [<ffffffff8107b55c>] warn_slowpath_fmt+0x5c/0x80 > [<ffffffff8130a0f1>] __list_del_entry+0xa1/0xd0 > [<ffffffff8121083c>] d_shrink_del+0x2c/0x80 > [<ffffffff81210fe5>] dentry_lru_del+0x25/0x30 > [<ffffffff812116f1>] dput+0x161/0x280 > [<ffffffff812057f5>] lookup_fast+0x275/0x2e0 > [<ffffffff8120833c>] path_lookupat+0x16c/0x7a0 > [<ffffffff81214dc7>] ? inode_init_always+0x107/0x1e0 > [<ffffffff811db380>] ? kmem_cache_alloc+0xf0/0x220 > [<ffffffff8120ab5f>] ? getname_flags+0x4f/0x1a0 > [<ffffffff8120899b>] filename_lookup+0x2b/0xc0 > [<ffffffff8120bc87>] user_path_at_empty+0x67/0xc0 > [<ffffffff81112962>] ? from_kgid_munged+0x12/0x20 > [<ffffffff811ff9e9>] ? cp_new_stat+0x149/0x180 > [<ffffffff8120bcf1>] user_path_at+0x11/0x20 > [<ffffffff811ff4f3>] vfs_fstatat+0x63/0xc0 > [<ffffffff811ffb04>] SYSC_newfstatat+0x24/0x60 > [<ffffffff8111c724>] ? __audit_syscall_entry+0xb4/0x110 > [<ffffffff81022923>] ? syscall_trace_enter+0x173/0x220 > [<ffffffff81640ff3>] ? tracesys+0x7e/0xe2 > [<ffffffff811ffd4e>] SyS_newfstatat+0xe/0x10 > [<ffffffff81641052>] tracesys+0xdd/0xe2 > > https://jira.sw.ru/browse/PSBM-44210 > > Signed-off-by: Vladimir Davydov <[email protected]> Ack-by: [email protected]
> ---
> fs/dcache.c | 31 ++++++++++---------------------
> 1 file changed, 10 insertions(+), 21 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 30d3d706f32e..cba54cf702f5 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1414,34 +1414,23 @@ static enum d_walk_ret select_collect(void *_data,
> struct dentry *dentry)
> if (data->start == dentry)
> goto out;
>
> - /*
> - * move only zero ref count dentries to the dispose list.
> - *
> - * Those which are presently on the shrink list, being processed
> - * by shrink_dentry_list(), shouldn't be moved. Otherwise the
> - * loop in shrink_dcache_parent() might not make any progress
> - * and loop forever.
> - */
> - if (dentry->d_lockref.count) {
> - dentry_lru_del(dentry);
> - } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
> - /*
> - * We can't use d_lru_shrink_move() because we
> - * need to get the global LRU lock and do the
> - * RLU accounting.
> - */
> - d_lru_del(dentry);
> - d_shrink_add(dentry, &data->dispose);
> + if (dentry->d_flags & DCACHE_SHRINK_LIST) {
> data->found++;
> - ret = D_WALK_NORETRY;
> + } else {
> + if (dentry->d_flags & DCACHE_LRU_LIST)
> + d_lru_del(dentry);
> + if (!dentry->d_lockref.count) {
> + d_shrink_add(dentry, &data->dispose);
> + data->found++;
> + }
> }
> /*
> * We can return to the caller if we have found some (this
> * ensures forward progress). We'll be coming back to find
> * the rest.
> */
> - if (data->found && need_resched())
> - ret = D_WALK_QUIT;
> + if (!list_empty(&data->dispose))
> + ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
> out:
> return ret;
> }
> --
> 2.1.4
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