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([2600:1700:6476:1430:f547:a2c0:72f7:6671]) by smtp.gmail.com with ESMTPSA id 00721157ae682-891f1b27c35sm10936237b3.46.2026.09.16.11.58.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Sep 2026 11:58:55 -0700 (PDT) Message-ID: <149f405e0e854092e6aa6470ac7e77f222d90fa0.camel@dubeyko.com> Subject: Re: [PATCH v2] nilfs2: fix checkpoint root lifetime on sysfs errors From: Viacheslav Dubeyko To: Aldo Ariel Panzardo , Ryusuke Konishi Cc: linux-nilfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Date: Wed, 16 Sep 2026 11:58:50 -0700 In-Reply-To: <20260915194958.3329611-1-qwe.aldo@gmail.com> References: <20260915041206.2430937-1-qwe.aldo@gmail.com> <20260915194958.3329611-1-qwe.aldo@gmail.com> Autocrypt: addr=slava@dubeyko.com; prefer-encrypt=mutual; keydata=mQINBGgaTLYBEADaJc/WqWTeunGetXyyGJ5Za7b23M/ozuDCWCp+yWUa2GqQKH40dxRIR zshgOmAue7t9RQJU9lxZ4ZHWbi1Hzz85+0omefEdAKFmxTO6+CYV0g/sapU0wPJws3sC2Pbda9/eJ ZcvScAX2n/PlhpTnzJKf3JkHh3nM1ACO3jzSe2/muSQJvqMLG2D71ccekr1RyUh8V+OZdrPtfkDam V6GOT6IvyE+d+55fzmo20nJKecvbyvdikWwZvjjCENsG9qOf3TcCJ9DDYwjyYe1To8b+mQM9nHcxp jUsUuH074BhISFwt99/htZdSgp4csiGeXr8f9BEotRB6+kjMBHaiJ6B7BIlDmlffyR4f3oR/5hxgy dvIxMocqyc03xVyM6tA4ZrshKkwDgZIFEKkx37ec22ZJczNwGywKQW2TGXUTZVbdooiG4tXbRBLxe ga/NTZ52ZdEkSxAUGw/l0y0InTtdDIWvfUT+WXtQcEPRBE6HHhoeFehLzWL/o7w5Hog+0hXhNjqte fzKpI2fWmYzoIb6ueNmE/8sP9fWXo6Av9m8B5hRvF/hVWfEysr/2LSqN+xjt9NEbg8WNRMLy/Y0MS p5fgf9pmGF78waFiBvgZIQNuQnHrM+0BmYOhR0JKoHjt7r5wLyNiKFc8b7xXndyCDYfniO3ljbr0j tXWRGxx4to6FwARAQABtCZWaWFjaGVzbGF2IER1YmV5a28gPHNsYXZhQGR1YmV5a28uY29tPokCVw QTAQoAQQIbAQUJA8JnAAULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBFXDC2tnzsoLQtrbBDlc2cL fhEB1BQJoGl5PAhkBAAoJEDlc2cLfhEB17DsP/jy/Dx19MtxWOniPqpQf2s65enkDZuMIQ94jSg7B F2qTKIbNR9SmsczjyjC+/J7m7WZRmcqnwFYMOyNfh12aF2WhjT7p5xEAbvfGVYwUpUrg/lcacdT0D Yk61GGc5ZB89OAWHLr0FJjI54bd7kn7E/JRQF4dqNsxU8qcPXQ0wLHxTHUPZu/w5Zu/cO+lQ3H0Pj pSEGaTAh+tBYGSvQ4YPYBcV8+qjTxzeNwkw4ARza8EjTwWKP2jWAfA/ay4VobRfqNQ2zLoo84qDtN Uxe0zPE2wobIXELWkbuW/6hoQFPpMlJWz+mbvVms57NAA1HO8F5c1SLFaJ6dN0AQbxrHi45/cQXla 9hSEOJjxcEnJG/ZmcomYHFneM9K1p1K6HcGajiY2BFWkVet9vuHygkLWXVYZ0lr1paLFR52S7T+cf 6dkxOqu1ZiRegvFoyzBUzlLh/elgp3tWUfG2VmJD3lGpB3m5ZhwQ3rFpK8A7cKzgKjwPp61Me0o9z HX53THoG+QG+o0nnIKK7M8+coToTSyznYoq9C3eKeM/J97x9+h9tbizaeUQvWzQOgG8myUJ5u5Dr4 6tv9KXrOJy0iy/dcyreMYV5lwODaFfOeA4Lbnn5vRn9OjuMg1PFhCi3yMI4lA4umXFw0V2/OI5rgW BQELhfvW6mxkihkl6KLZX8m1zcHitCpWaWFjaGVzbGF2IER1YmV5a28gPFNsYXZhLkR1YmV5a29Aa WJtLmNvbT6JAlQEEwEKAD4WIQRVwwtrZ87KC0La2wQ5XNnC34RAdQUCaBpd7AIbAQUJA8JnAAULCQ gHAgYVCgkICwIEFgIDAQIeAQIXgAAKCRA5XNnC34RAdYjFEACiWBEybMt1xjRbEgaZ3UP5i2bSway DwYDvgWW5EbRP7JcqOcZ2vkJwrK3gsqC3FKpjOPh7ecE0I4vrabH1Qobe2N8B2Y396z24mGnkTBbb 16Uz3PC93nFN1BA0wuOjlr1/oOTy5gBY563vybhnXPfSEUcXRd28jI7z8tRyzXh2tL8ZLdv1u4vQ8 E0O7lVJ55p9yGxbwgb5vXU4T2irqRKLxRvU80rZIXoEM7zLf5r7RaRxgwjTKdu6rYMUOfoyEQQZTD 4Xg9YE/X8pZzcbYFs4IlscyK6cXU0pjwr2ssjearOLLDJ7ygvfOiOuCZL+6zHRunLwq2JH/RmwuLV mWWSbgosZD6c5+wu6DxV15y7zZaR3NFPOR5ErpCFUorKzBO1nA4dwOAbNym9OGkhRgLAyxwpea0V0 ZlStfp0kfVaSZYo7PXd8Bbtyjali0niBjPpEVZdgtVUpBlPr97jBYZ+L5GF3hd6WJFbEYgj+5Af7C UjbX9DHweGQ/tdXWRnJHRzorxzjOS3003ddRnPtQDDN3Z/XzdAZwQAs0RqqXrTeeJrLppFUbAP+HZ TyOLVJcAAlVQROoq8PbM3ZKIaOygjj6Yw0emJi1D9OsN2UKjoe4W185vamFWX4Ba41jmCPrYJWAWH fAMjjkInIPg7RLGs8FiwxfcpkILP0YbVWHiNAabQoVmlhY2hlc2xhdiBEdWJleWtvIDx2ZHViZXlr b0BrZXJuZWwub3JnPokCVAQTAQoAPhYhBFXDC2tnzsoLQtrbBDlc2cLfhEB1BQJoVemuAhsBBQkDw mcABQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEDlc2cLfhEB1GRwP/1scX5HO9Sk7dRicLD/fxo ipwEs+UbeA0/TM8OQfdRI4C/tFBYbQCR7lD05dfq8VsYLEyrgeLqP/iRhabLky8LTaEdwoAqPDc/O 9HRffx/faJZqkKc1dZryjqS6b8NExhKOVWmDqN357+Cl/H4hT9wnvjCj1YEqXIxSd/2Pc8+yw/KRC AP7jtRzXHcc/49Lpz/NU5irScusxy2GLKa5o/13jFK3F1fWX1wsOJF8NlTx3rLtBy4GWHITwkBmu8 zI4qcJGp7eudI0l4xmIKKQWanEhVdzBm5UnfyLIa7gQ2T48UbxJlWnMhLxMPrxgtC4Kos1G3zovEy Ep+fJN7D1pwN9aR36jVKvRsX7V4leIDWGzCdfw1FGWkMUfrRwgIl6i3wgqcCP6r9YSWVQYXdmwdMu 1RFLC44iF9340S0hw9+30yGP8TWwd1mm8V/+zsdDAFAoAwisi5QLLkQnEsJSgLzJ9daAsE8KjMthv hUWHdpiUSjyCpigT+KPl9YunZhyrC1jZXERCDPCQVYgaPt+Xbhdjcem/ykv8UVIDAGVXjuk4OW8la nf8SP+uxkTTDKcPHOa5rYRaeNj7T/NClRSd4z6aV3F6pKEJnEGvv/DFMXtSHlbylhyiGKN2Amd0b4 9jg+DW85oNN7q2UYzYuPwkHsFFq5iyF1QggiwYYTpoVXsw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (by Flathub.org) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-09-15 at 16:49 -0300, Aldo Ariel Panzardo wrote: > nilfs_find_or_create_root() publishes a new root in the checkpoint > tree before creating its sysfs object.=C2=A0 If sysfs registration fails, > the root is freed while it is still reachable from the tree.=C2=A0 A > concurrent nilfs_lookup_root() can then dereference freed memory. >=20 > The fix needs the lock to be held across the sysfs call, but > nilfs_sysfs_create_snapshot_group() can sleep, so the existing > spinlock is not suitable. >=20 > Convert ns_cptree_lock from a spinlock to a mutex.=C2=A0 All existing > callers are in process context (mount, lookup, segctor, recovery), > and nilfs_put_root() can use refcount_dec_and_mutex_lock() as the > atomic decrement-and-acquire primitive. >=20 > With the mutex, nilfs_find_or_create_root() can hold it across the > sysfs registration and only insert the root into the rbtree after > sysfs succeeds.=C2=A0 On failure, the root was never visible and can be > freed after waiting for the kobject release callback to complete. >=20 > Both the creation error path and the normal removal path must wait > for the embedded kobject release via wait_for_completion() before > freeing the container, because kobject_put() does not guarantee > synchronous release (CONFIG_DEBUG_KOBJECT_RELEASE defers it). >=20 > Fixes: dd70edbde262 ("nilfs2: integrate sysfs support into driver") > Cc: stable@vger.kernel.org > Signed-off-by: Aldo Ariel Panzardo > --- >=20 > Changes in v2: > =C2=A0 - Convert ns_cptree_lock from spinlock to mutex instead of adding > =C2=A0=C2=A0=C2=A0 a second lock, as suggested by Viacheslav Dubeyko.=C2= =A0 Use > =C2=A0=C2=A0=C2=A0 refcount_dec_and_mutex_lock() in nilfs_put_root(). >=20 > =C2=A0fs/nilfs2/the_nilfs.c | 35 +++++++++++++++++++---------------- > =C2=A0fs/nilfs2/the_nilfs.h |=C2=A0 2 +- > =C2=A02 files changed, 20 insertions(+), 17 deletions(-) >=20 > diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c > index 7b23e373a1..5bfa853471 100644 > --- a/fs/nilfs2/the_nilfs.c > +++ b/fs/nilfs2/the_nilfs.c > @@ -70,7 +70,7 @@ struct the_nilfs *alloc_nilfs(struct super_block > *sb) > =C2=A0 spin_lock_init(&nilfs->ns_inode_lock); > =C2=A0 spin_lock_init(&nilfs->ns_last_segment_lock); > =C2=A0 nilfs->ns_cptree =3D RB_ROOT; > - spin_lock_init(&nilfs->ns_cptree_lock); > + mutex_init(&nilfs->ns_cptree_lock); > =C2=A0 init_rwsem(&nilfs->ns_segctor_sem); > =C2=A0 nilfs->ns_sb_update_freq =3D NILFS_SB_FREQ; > =C2=A0 > @@ -846,7 +846,7 @@ struct nilfs_root *nilfs_lookup_root(struct > the_nilfs *nilfs, __u64 cno) > =C2=A0 struct rb_node *n; > =C2=A0 struct nilfs_root *root; > =C2=A0 > - spin_lock(&nilfs->ns_cptree_lock); > + mutex_lock(&nilfs->ns_cptree_lock); > =C2=A0 n =3D nilfs->ns_cptree.rb_node; > =C2=A0 while (n) { > =C2=A0 root =3D rb_entry(n, struct nilfs_root, rb_node); > @@ -857,11 +857,11 @@ struct nilfs_root *nilfs_lookup_root(struct > the_nilfs *nilfs, __u64 cno) > =C2=A0 n =3D n->rb_right; > =C2=A0 } else { > =C2=A0 refcount_inc(&root->count); > - spin_unlock(&nilfs->ns_cptree_lock); > + mutex_unlock(&nilfs->ns_cptree_lock); > =C2=A0 return root; > =C2=A0 } > =C2=A0 } > - spin_unlock(&nilfs->ns_cptree_lock); > + mutex_unlock(&nilfs->ns_cptree_lock); > =C2=A0 > =C2=A0 return NULL; > =C2=A0} > @@ -881,7 +881,7 @@ nilfs_find_or_create_root(struct the_nilfs > *nilfs, __u64 cno) > =C2=A0 if (!new) > =C2=A0 return NULL; > =C2=A0 > - spin_lock(&nilfs->ns_cptree_lock); > + mutex_lock(&nilfs->ns_cptree_lock); > =C2=A0 > =C2=A0 p =3D &nilfs->ns_cptree.rb_node; > =C2=A0 parent =3D NULL; > @@ -896,7 +896,7 @@ nilfs_find_or_create_root(struct the_nilfs > *nilfs, __u64 cno) > =C2=A0 p =3D &(*p)->rb_right; > =C2=A0 } else { > =C2=A0 refcount_inc(&root->count); > - spin_unlock(&nilfs->ns_cptree_lock); > + mutex_unlock(&nilfs->ns_cptree_lock); > =C2=A0 kfree(new); > =C2=A0 return root; > =C2=A0 } > @@ -909,17 +909,19 @@ nilfs_find_or_create_root(struct the_nilfs > *nilfs, __u64 cno) > =C2=A0 atomic64_set(&new->inodes_count, 0); > =C2=A0 atomic64_set(&new->blocks_count, 0); > =C2=A0 > - rb_link_node(&new->rb_node, parent, p); > - rb_insert_color(&new->rb_node, &nilfs->ns_cptree); > - > - spin_unlock(&nilfs->ns_cptree_lock); > - > =C2=A0 err =3D nilfs_sysfs_create_snapshot_group(new); > =C2=A0 if (err) { > + mutex_unlock(&nilfs->ns_cptree_lock); > + wait_for_completion(&new->snapshot_kobj_unregister); > =C2=A0 kfree(new); > - new =3D NULL; > + return NULL; > =C2=A0 } > =C2=A0 > + rb_link_node(&new->rb_node, parent, p); > + rb_insert_color(&new->rb_node, &nilfs->ns_cptree); > + > + mutex_unlock(&nilfs->ns_cptree_lock); > + > =C2=A0 return new; > =C2=A0} > =C2=A0 > @@ -927,13 +929,14 @@ void nilfs_put_root(struct nilfs_root *root) > =C2=A0{ > =C2=A0 struct the_nilfs *nilfs =3D root->nilfs; > =C2=A0 > - if (refcount_dec_and_lock(&root->count, &nilfs- > >ns_cptree_lock)) { > + if (refcount_dec_and_mutex_lock(&root->count, > + &nilfs->ns_cptree_lock)) { > =C2=A0 rb_erase(&root->rb_node, &nilfs->ns_cptree); > - spin_unlock(&nilfs->ns_cptree_lock); > - > =C2=A0 nilfs_sysfs_delete_snapshot_group(root); > - iput(root->ifile); > + wait_for_completion(&root- > >snapshot_kobj_unregister); Is it right behavior that we are waiting completion under the lock? Could we have potential deadlock here? I am feeling slightly bad about waiting something under the lock. > + mutex_unlock(&nilfs->ns_cptree_lock); > =C2=A0 > + iput(root->ifile); > =C2=A0 kfree(root); > =C2=A0 } > =C2=A0} > diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h > index 4776a70f01..074644c64a 100644 > --- a/fs/nilfs2/the_nilfs.h > +++ b/fs/nilfs2/the_nilfs.h > @@ -150,7 +150,7 @@ struct the_nilfs { > =C2=A0 > =C2=A0 /* Checkpoint tree */ > =C2=A0 struct rb_root ns_cptree; > - spinlock_t ns_cptree_lock; > + struct mutex ns_cptree_lock; /* Protects > ns_cptree */ I assume that you prefer mutex because of exclusive lock nature. Could we improve something for the case of rw_semaphore? Thanks, Slava. > =C2=A0 > =C2=A0 /* Dirty inode list */ > =C2=A0 struct list_head ns_dirty_files;