Re: 3ba75830ce ("nfsd4: drc containerization"): [ 51.013875] WARNING: possible circular locking dependency detected
From: J. Bruce Fields
Date: Tue Jun 02 2020 - 14:30:10 EST
On Wed, May 27, 2020 at 01:11:59PM +0800, kernel test robot wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> commit 3ba75830ce175550ef45c6524ec62faab8f62c1b
Thanks! I looked at the code quickly and can't figure out where the
deadlock is exactly.
It seems to involve the kmem_cache_create() call in nfsd's net init
method. Anyone know if there's a reason why creating a new slab cache
during network namespace initialization is a potential deadlock?
It was probably a dumb thing to do in this case--I can apply the below
to make the slab global again. Kinda curious what exactly the bug is,
though.
--b.
commit 027690c75e8f
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date: Mon Jun 1 17:44:45 2020 -0400
nfsd4: make drc_slab global, not per-net
I made every global per-network-namespace instead. But perhaps doing
that to this slab was a step too far.
The kmem_cache_create call in our net init method also seems to be
responsible for this lockdep warning:
[ 45.163710] Unable to find swap-space signature
[ 45.375718] trinity-c1 (855): attempted to duplicate a private mapping with mremap. This is not supported.
[ 46.055744] futex_wake_op: trinity-c1 tries to shift op by -209; fix this program
[ 51.011723]
[ 51.013378] ======================================================
[ 51.013875] WARNING: possible circular locking dependency detected
[ 51.014378] 5.2.0-rc2 #1 Not tainted
[ 51.014672] ------------------------------------------------------
[ 51.015182] trinity-c2/886 is trying to acquire lock:
[ 51.015593] 000000005405f099 (slab_mutex){+.+.}, at: slab_attr_store+0xa2/0x130
[ 51.016190]
[ 51.016190] but task is already holding lock:
[ 51.016652] 00000000ac662005 (kn->count#43){++++}, at: kernfs_fop_write+0x286/0x500
[ 51.017266]
[ 51.017266] which lock already depends on the new lock.
[ 51.017266]
[ 51.017909]
[ 51.017909] the existing dependency chain (in reverse order) is:
[ 51.018497]
[ 51.018497] -> #1 (kn->count#43){++++}:
[ 51.018956] __lock_acquire+0x7cf/0x1a20
[ 51.019317] lock_acquire+0x17d/0x390
[ 51.019658] __kernfs_remove+0x892/0xae0
[ 51.020020] kernfs_remove_by_name_ns+0x78/0x110
[ 51.020435] sysfs_remove_link+0x55/0xb0
[ 51.020832] sysfs_slab_add+0xc1/0x3e0
[ 51.021332] __kmem_cache_create+0x155/0x200
[ 51.021720] create_cache+0xf5/0x320
[ 51.022054] kmem_cache_create_usercopy+0x179/0x320
[ 51.022486] kmem_cache_create+0x1a/0x30
[ 51.022867] nfsd_reply_cache_init+0x278/0x560
[ 51.023266] nfsd_init_net+0x20f/0x5e0
[ 51.023623] ops_init+0xcb/0x4b0
[ 51.023928] setup_net+0x2fe/0x670
[ 51.024315] copy_net_ns+0x30a/0x3f0
[ 51.024653] create_new_namespaces+0x3c5/0x820
[ 51.025257] unshare_nsproxy_namespaces+0xd1/0x240
[ 51.025881] ksys_unshare+0x506/0x9c0
[ 51.026381] __x64_sys_unshare+0x3a/0x50
[ 51.026937] do_syscall_64+0x110/0x10b0
[ 51.027509] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 51.028175]
[ 51.028175] -> #0 (slab_mutex){+.+.}:
[ 51.028817] validate_chain+0x1c51/0x2cc0
[ 51.029422] __lock_acquire+0x7cf/0x1a20
[ 51.029947] lock_acquire+0x17d/0x390
[ 51.030438] __mutex_lock+0x100/0xfa0
[ 51.030995] mutex_lock_nested+0x27/0x30
[ 51.031516] slab_attr_store+0xa2/0x130
[ 51.032020] sysfs_kf_write+0x11d/0x180
[ 51.032529] kernfs_fop_write+0x32a/0x500
[ 51.033056] do_loop_readv_writev+0x21d/0x310
[ 51.033627] do_iter_write+0x2e5/0x380
[ 51.034148] vfs_writev+0x170/0x310
[ 51.034616] do_pwritev+0x13e/0x160
[ 51.035100] __x64_sys_pwritev+0xa3/0x110
[ 51.035633] do_syscall_64+0x110/0x10b0
[ 51.036200] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 51.036924]
[ 51.036924] other info that might help us debug this:
[ 51.036924]
[ 51.037876] Possible unsafe locking scenario:
[ 51.037876]
[ 51.038556] CPU0 CPU1
[ 51.039130] ---- ----
[ 51.039676] lock(kn->count#43);
[ 51.040084] lock(slab_mutex);
[ 51.040597] lock(kn->count#43);
[ 51.041062] lock(slab_mutex);
[ 51.041320]
[ 51.041320] *** DEADLOCK ***
[ 51.041320]
[ 51.041793] 3 locks held by trinity-c2/886:
[ 51.042128] #0: 000000001f55e152 (sb_writers#5){.+.+}, at: vfs_writev+0x2b9/0x310
[ 51.042739] #1: 00000000c7d6c034 (&of->mutex){+.+.}, at: kernfs_fop_write+0x25b/0x500
[ 51.043400] #2: 00000000ac662005 (kn->count#43){++++}, at: kernfs_fop_write+0x286/0x500
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Fixes: 3ba75830ce17 "drc containerization"
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
index 10ec5ecdf117..65c331f75e9c 100644
--- a/fs/nfsd/cache.h
+++ b/fs/nfsd/cache.h
@@ -78,6 +78,8 @@ enum {
/* Checksum this amount of the request */
#define RC_CSUMLEN (256U)
+int nfsd_drc_slab_create(void);
+void nfsd_drc_slab_free(void);
int nfsd_reply_cache_init(struct nfsd_net *);
void nfsd_reply_cache_shutdown(struct nfsd_net *);
int nfsd_cache_lookup(struct svc_rqst *);
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 09aa545825bd..9217cb64bf0e 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -139,7 +139,6 @@ struct nfsd_net {
* Duplicate reply cache
*/
struct nfsd_drc_bucket *drc_hashtbl;
- struct kmem_cache *drc_slab;
/* max number of entries allowed in the cache */
unsigned int max_drc_entries;
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 945d2f5e760e..f30a7def7899 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -35,6 +35,8 @@ struct nfsd_drc_bucket {
spinlock_t cache_lock;
};
+static struct kmem_cache *drc_slab;
+
static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
struct shrink_control *sc);
@@ -94,7 +96,7 @@ nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum,
{
struct svc_cacherep *rp;
- rp = kmem_cache_alloc(nn->drc_slab, GFP_KERNEL);
+ rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
if (rp) {
rp->c_state = RC_UNUSED;
rp->c_type = RC_NOCACHE;
@@ -128,7 +130,7 @@ nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
atomic_dec(&nn->num_drc_entries);
nn->drc_mem_usage -= sizeof(*rp);
}
- kmem_cache_free(nn->drc_slab, rp);
+ kmem_cache_free(drc_slab, rp);
}
static void
@@ -140,6 +142,18 @@ nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
spin_unlock(&b->cache_lock);
}
+int nfsd_drc_slab_create(void)
+{
+ drc_slab = kmem_cache_create("nfsd_drc",
+ sizeof(struct svc_cacherep), 0, 0, NULL);
+ return drc_slab ? 0: -ENOMEM;
+}
+
+void nfsd_drc_slab_free(void)
+{
+ kmem_cache_destroy(drc_slab);
+}
+
int nfsd_reply_cache_init(struct nfsd_net *nn)
{
unsigned int hashsize;
@@ -158,18 +172,13 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
if (status)
goto out_nomem;
- nn->drc_slab = kmem_cache_create("nfsd_drc",
- sizeof(struct svc_cacherep), 0, 0, NULL);
- if (!nn->drc_slab)
- goto out_shrinker;
-
nn->drc_hashtbl = kcalloc(hashsize,
sizeof(*nn->drc_hashtbl), GFP_KERNEL);
if (!nn->drc_hashtbl) {
nn->drc_hashtbl = vzalloc(array_size(hashsize,
sizeof(*nn->drc_hashtbl)));
if (!nn->drc_hashtbl)
- goto out_slab;
+ goto out_shrinker;
}
for (i = 0; i < hashsize; i++) {
@@ -179,8 +188,6 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
nn->drc_hashsize = hashsize;
return 0;
-out_slab:
- kmem_cache_destroy(nn->drc_slab);
out_shrinker:
unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
out_nomem:
@@ -208,8 +215,6 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
nn->drc_hashtbl = NULL;
nn->drc_hashsize = 0;
- kmem_cache_destroy(nn->drc_slab);
- nn->drc_slab = NULL;
}
/*
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index b48eac3bb72b..b68e96681522 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1533,6 +1533,9 @@ static int __init init_nfsd(void)
goto out_free_slabs;
nfsd_fault_inject_init(); /* nfsd fault injection controls */
nfsd_stat_init(); /* Statistics */
+ retval = nfsd_drc_slab_create();
+ if (retval)
+ goto out_free_stat;
nfsd_lockd_init(); /* lockd->nfsd callbacks */
retval = create_proc_exports_entry();
if (retval)
@@ -1546,6 +1549,8 @@ static int __init init_nfsd(void)
remove_proc_entry("fs/nfs", NULL);
out_free_lockd:
nfsd_lockd_shutdown();
+ nfsd_drc_slab_free();
+out_free_stat:
nfsd_stat_shutdown();
nfsd_fault_inject_cleanup();
nfsd4_exit_pnfs();
@@ -1560,6 +1565,7 @@ static int __init init_nfsd(void)
static void __exit exit_nfsd(void)
{
+ nfsd_drc_slab_free();
remove_proc_entry("fs/nfs/exports", NULL);
remove_proc_entry("fs/nfs", NULL);
nfsd_stat_shutdown();