6.6-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo tj@kernel.org
commit e3977e0609a07d86406029fceea0fd40d7849368 upstream.
This reverts commit dad3fb67ca1cbef87ce700e83a55835e5921ce8a.
The commit converted kernfs_idr_lock to an IRQ-safe raw_spinlock because it could be acquired while holding an rq lock through bpf_cgroup_from_id(). However, kernfs_idr_lock is held while doing GPF_NOWAIT allocations which involves acquiring an non-IRQ-safe and non-raw lock leading to the following lockdep warning:
============================= [ BUG: Invalid wait context ] 6.7.0-rc5-kzm9g-00251-g655022a45b1c #578 Not tainted ----------------------------- swapper/0/0 is trying to lock: dfbcd488 (&c->lock){....}-{3:3}, at: local_lock_acquire+0x0/0xa4 other info that might help us debug this: context-{5:5} 2 locks held by swapper/0/0: #0: dfbc9c60 (lock){+.+.}-{3:3}, at: local_lock_acquire+0x0/0xa4 #1: c0c012a8 (kernfs_idr_lock){....}-{2:2}, at: __kernfs_new_node.constprop.0+0x68/0x258 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.7.0-rc5-kzm9g-00251-g655022a45b1c #578 Hardware name: Generic SH73A0 (Flattened Device Tree) unwind_backtrace from show_stack+0x10/0x14 show_stack from dump_stack_lvl+0x68/0x90 dump_stack_lvl from __lock_acquire+0x3cc/0x168c __lock_acquire from lock_acquire+0x274/0x30c lock_acquire from local_lock_acquire+0x28/0xa4 local_lock_acquire from ___slab_alloc+0x234/0x8a8 ___slab_alloc from __slab_alloc.constprop.0+0x30/0x44 __slab_alloc.constprop.0 from kmem_cache_alloc+0x7c/0x148 kmem_cache_alloc from radix_tree_node_alloc.constprop.0+0x44/0xdc radix_tree_node_alloc.constprop.0 from idr_get_free+0x110/0x2b8 idr_get_free from idr_alloc_u32+0x9c/0x108 idr_alloc_u32 from idr_alloc_cyclic+0x50/0xb8 idr_alloc_cyclic from __kernfs_new_node.constprop.0+0x88/0x258 __kernfs_new_node.constprop.0 from kernfs_create_root+0xbc/0x154 kernfs_create_root from sysfs_init+0x18/0x5c sysfs_init from mnt_init+0xc4/0x220 mnt_init from vfs_caches_init+0x6c/0x88 vfs_caches_init from start_kernel+0x474/0x528 start_kernel from 0x0
Let's rever the commit. It's undesirable to spread out raw spinlock usage anyway and the problem can be solved by protecting the lookup path with RCU instead.
Signed-off-by: Tejun Heo tj@kernel.org Cc: Andrea Righi andrea.righi@canonical.com Reported-by: Geert Uytterhoeven geert@linux-m68k.org Link: http://lkml.kernel.org/r/CAMuHMdV=AKt+mwY7svEq5gFPx41LoSQZ_USME5_MEdWQze13ww... Link: https://lore.kernel.org/r/20240109214828.252092-2-tj@kernel.org Tested-by: Andrea Righi andrea.righi@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/kernfs/dir.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-)
--- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -27,7 +27,7 @@ static DEFINE_RWLOCK(kernfs_rename_lock) */ static DEFINE_SPINLOCK(kernfs_pr_cont_lock); static char kernfs_pr_cont_buf[PATH_MAX]; /* protected by pr_cont_lock */ -static DEFINE_RAW_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */ +static DEFINE_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */
#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
@@ -539,7 +539,6 @@ void kernfs_put(struct kernfs_node *kn) { struct kernfs_node *parent; struct kernfs_root *root; - unsigned long flags;
if (!kn || !atomic_dec_and_test(&kn->count)) return; @@ -564,9 +563,9 @@ void kernfs_put(struct kernfs_node *kn) simple_xattrs_free(&kn->iattr->xattrs, NULL); kmem_cache_free(kernfs_iattrs_cache, kn->iattr); } - raw_spin_lock_irqsave(&kernfs_idr_lock, flags); + spin_lock(&kernfs_idr_lock); idr_remove(&root->ino_idr, (u32)kernfs_ino(kn)); - raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); + spin_unlock(&kernfs_idr_lock); kmem_cache_free(kernfs_node_cache, kn);
kn = parent; @@ -608,7 +607,6 @@ static struct kernfs_node *__kernfs_new_ struct kernfs_node *kn; u32 id_highbits; int ret; - unsigned long irqflags;
name = kstrdup_const(name, GFP_KERNEL); if (!name) @@ -619,13 +617,13 @@ static struct kernfs_node *__kernfs_new_ goto err_out1;
idr_preload(GFP_KERNEL); - raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags); + spin_lock(&kernfs_idr_lock); ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC); if (ret >= 0 && ret < root->last_id_lowbits) root->id_highbits++; id_highbits = root->id_highbits; root->last_id_lowbits = ret; - raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags); + spin_unlock(&kernfs_idr_lock); idr_preload_end(); if (ret < 0) goto err_out2; @@ -661,9 +659,9 @@ static struct kernfs_node *__kernfs_new_ return kn;
err_out3: - raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags); + spin_lock(&kernfs_idr_lock); idr_remove(&root->ino_idr, (u32)kernfs_ino(kn)); - raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags); + spin_unlock(&kernfs_idr_lock); err_out2: kmem_cache_free(kernfs_node_cache, kn); err_out1: @@ -704,9 +702,8 @@ struct kernfs_node *kernfs_find_and_get_ struct kernfs_node *kn; ino_t ino = kernfs_id_ino(id); u32 gen = kernfs_id_gen(id); - unsigned long flags;
- raw_spin_lock_irqsave(&kernfs_idr_lock, flags); + spin_lock(&kernfs_idr_lock);
kn = idr_find(&root->ino_idr, (u32)ino); if (!kn) @@ -730,10 +727,10 @@ struct kernfs_node *kernfs_find_and_get_ if (unlikely(!__kernfs_active(kn) || !atomic_inc_not_zero(&kn->count))) goto err_unlock;
- raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); + spin_unlock(&kernfs_idr_lock); return kn; err_unlock: - raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); + spin_unlock(&kernfs_idr_lock); return NULL; }