kernfs: Move faulting copy_user operations outside of the mutex
A fault in a user provided buffer may lead anywhere, and lockdep warns
that we have a potential deadlock between the mm->mmap_sem and the
kernfs file mutex:
[ 82.811702] ======================================================
[ 82.811705] [ INFO: possible circular locking dependency detected ]
[ 82.811709] 4.5.0-rc4-gfxbench+ #1 Not tainted
[ 82.811711] -------------------------------------------------------
[ 82.811714] kms_setmode/5859 is trying to acquire lock:
[ 82.811717] (&dev->struct_mutex){+.+.+.}, at: [<ffffffff8150d9c1>] drm_gem_mmap+0x1a1/0x270
[ 82.811731]
but task is already holding lock:
[ 82.811734] (&mm->mmap_sem){++++++}, at: [<ffffffff8117b364>] vm_mmap_pgoff+0x44/0xa0
[ 82.811745]
which lock already depends on the new lock.
[ 82.811749]
the existing dependency chain (in reverse order) is:
[ 82.811752]
-> #3 (&mm->mmap_sem){++++++}:
[ 82.811761] [<ffffffff810cc883>] lock_acquire+0xc3/0x1d0
[ 82.811766] [<ffffffff8118bc65>] __might_fault+0x75/0xa0
[ 82.811771] [<ffffffff8124da4a>] kernfs_fop_write+0x8a/0x180
[ 82.811787] [<ffffffff811d1023>] __vfs_write+0x23/0xe0
[ 82.811792] [<ffffffff811d1d74>] vfs_write+0xa4/0x190
[ 82.811797] [<ffffffff811d2c14>] SyS_write+0x44/0xb0
[ 82.811801] [<ffffffff817bb81b>] entry_SYSCALL_64_fastpath+0x16/0x73
[ 82.811807]
-> #2 (s_active#6){++++.+}:
[ 82.811814] [<ffffffff810cc883>] lock_acquire+0xc3/0x1d0
[ 82.811819] [<ffffffff8124c070>] __kernfs_remove+0x210/0x2f0
[ 82.811823] [<ffffffff8124d040>] kernfs_remove_by_name_ns+0x40/0xa0
[ 82.811828] [<ffffffff8124e9e0>] sysfs_remove_file_ns+0x10/0x20
[ 82.811832] [<ffffffff815318d4>] device_del+0x124/0x250
[ 82.811837] [<ffffffff81531a19>] device_unregister+0x19/0x60
[ 82.811841] [<ffffffff8153c051>] cpu_cache_sysfs_exit+0x51/0xb0
[ 82.811846] [<ffffffff8153c628>] cacheinfo_cpu_callback+0x38/0x70
[ 82.811851] [<ffffffff8109ae89>] notifier_call_chain+0x39/0xa0
[ 82.811856] [<ffffffff8109aef9>] __raw_notifier_call_chain+0x9/0x10
[ 82.811860] [<ffffffff810786de>] cpu_notify+0x1e/0x40
[ 82.811865] [<ffffffff81078779>] cpu_notify_nofail+0x9/0x20
[ 82.811869] [<ffffffff81078ac3>] _cpu_down+0x233/0x340
[ 82.811874] [<ffffffff81079019>] disable_nonboot_cpus+0xc9/0x350
[ 82.811878] [<ffffffff810d2e11>] suspend_devices_and_enter+0x5a1/0xb50
[ 82.811883] [<ffffffff810d3903>] pm_suspend+0x543/0x8d0
[ 82.811888] [<ffffffff810d1b77>] state_store+0x77/0xe0
[ 82.811892] [<ffffffff813fa68f>] kobj_attr_store+0xf/0x20
[ 82.811897] [<ffffffff8124e740>] sysfs_kf_write+0x40/0x50
[ 82.811902] [<ffffffff8124dafc>] kernfs_fop_write+0x13c/0x180
[ 82.811906] [<ffffffff811d1023>] __vfs_write+0x23/0xe0
[ 82.811910] [<ffffffff811d1d74>] vfs_write+0xa4/0x190
[ 82.811914] [<ffffffff811d2c14>] SyS_write+0x44/0xb0
[ 82.811918] [<ffffffff817bb81b>] entry_SYSCALL_64_fastpath+0x16/0x73
[ 82.811923]
-> #1 (cpu_hotplug.lock){+.+.+.}:
[ 82.811929] [<ffffffff810cc883>] lock_acquire+0xc3/0x1d0
[ 82.811933] [<ffffffff817b6f72>] mutex_lock_nested+0x62/0x3b0
[ 82.811940] [<ffffffff810784c1>] get_online_cpus+0x61/0x80
[ 82.811944] [<ffffffff811170eb>] stop_machine+0x1b/0xe0
[ 82.811949] [<ffffffffa0178edd>] gen8_ggtt_insert_entries__BKL+0x2d/0x30 [i915]
[ 82.812009] [<ffffffffa017d3a6>] ggtt_bind_vma+0x46/0x70 [i915]
[ 82.812045] [<ffffffffa017eb70>] i915_vma_bind+0x140/0x290 [i915]
[ 82.812081] [<ffffffffa01862b9>] i915_gem_object_do_pin+0x899/0xb00 [i915]
[ 82.812117] [<ffffffffa0186555>] i915_gem_object_pin+0x35/0x40 [i915]
[ 82.812154] [<ffffffffa019a23e>] intel_init_pipe_control+0xbe/0x210 [i915]
[ 82.812192] [<ffffffffa0197312>] intel_logical_rings_init+0xe2/0xde0 [i915]
[ 82.812232] [<ffffffffa0186fe3>] i915_gem_init+0xf3/0x130 [i915]
[ 82.812278] [<ffffffffa02097ed>] i915_driver_load+0xf2d/0x1770 [i915]
[ 82.812318] [<ffffffff81512474>] drm_dev_register+0xa4/0xb0
[ 82.812323] [<ffffffff8151467e>] drm_get_pci_dev+0xce/0x1e0
[ 82.812328] [<ffffffffa01472cf>] i915_pci_probe+0x2f/0x50 [i915]
[ 82.812360] [<ffffffff8143f907>] pci_device_probe+0x87/0xf0
[ 82.812366] [<ffffffff81535f89>] driver_probe_device+0x229/0x450
[ 82.812371] [<ffffffff81536233>] __driver_attach+0x83/0x90
[ 82.812375] [<ffffffff81533c61>] bus_for_each_dev+0x61/0xa0
[ 82.812380] [<ffffffff81535879>] driver_attach+0x19/0x20
[ 82.812384] [<ffffffff8153535f>] bus_add_driver+0x1ef/0x290
[ 82.812388] [<ffffffff81536e9b>] driver_register+0x5b/0xe0
[ 82.812393] [<ffffffff8143e83b>] __pci_register_driver+0x5b/0x60
[ 82.812398] [<ffffffff81514866>] drm_pci_init+0xd6/0x100
[ 82.812402] [<ffffffffa027c094>] 0xffffffffa027c094
[ 82.812406] [<ffffffff810003de>] do_one_initcall+0xae/0x1d0
[ 82.812412] [<ffffffff811595a0>] do_init_module+0x5b/0x1cb
[ 82.812417] [<ffffffff81106160>] load_module+0x1c20/0x2480
[ 82.812422] [<ffffffff81106bae>] SyS_finit_module+0x7e/0xa0
[ 82.812428] [<ffffffff817bb81b>] entry_SYSCALL_64_fastpath+0x16/0x73
[ 82.812433]
-> #0 (&dev->struct_mutex){+.+.+.}:
[ 82.812439] [<ffffffff810cbe59>] __lock_acquire+0x1fc9/0x20f0
[ 82.812443] [<ffffffff810cc883>] lock_acquire+0xc3/0x1d0
[ 82.812456] [<ffffffff8150d9e7>] drm_gem_mmap+0x1c7/0x270
[ 82.812460] [<ffffffff81196a14>] mmap_region+0x334/0x580
[ 82.812466] [<ffffffff81196fc4>] do_mmap+0x364/0x410
[ 82.812470] [<ffffffff8117b38d>] vm_mmap_pgoff+0x6d/0xa0
[ 82.812474] [<ffffffff811950f4>] SyS_mmap_pgoff+0x184/0x220
[ 82.812479] [<ffffffff8100a0fd>] SyS_mmap+0x1d/0x20
[ 82.812484] [<ffffffff817bb81b>] entry_SYSCALL_64_fastpath+0x16/0x73
[ 82.812489]
other info that might help us debug this:
[ 82.812493] Chain exists of:
&dev->struct_mutex --> s_active#6 --> &mm->mmap_sem
[ 82.812502] Possible unsafe locking scenario:
[ 82.812506] CPU0 CPU1
[ 82.812508] ---- ----
[ 82.812510] lock(&mm->mmap_sem);
[ 82.812514] lock(s_active#6);
[ 82.812519] lock(&mm->mmap_sem);
[ 82.812522] lock(&dev->struct_mutex);
[ 82.812526]
*** DEADLOCK ***
[ 82.812531] 1 lock held by kms_setmode/5859:
[ 82.812533] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8117b364>] vm_mmap_pgoff+0x44/0xa0
[ 82.812541]
stack backtrace:
[ 82.812547] CPU: 0 PID: 5859 Comm: kms_setmode Not tainted 4.5.0-rc4-gfxbench+ #1
[ 82.812550] Hardware name: /NUC5CPYB, BIOS PYBSWCEL.86A.0040.2015.0814.1353 08/14/2015
[ 82.812553] 0000000000000000 ffff880079407bf0 ffffffff813f8505 ffffffff825fb270
[ 82.812560] ffffffff825c4190 ffff880079407c30 ffffffff810c84ac ffff880079407c90
[ 82.812566] ffff8800797ed328 ffff8800797ecb00 0000000000000001 ffff8800797ed350
[ 82.812573] Call Trace:
[ 82.812578] [<ffffffff813f8505>] dump_stack+0x67/0x92
[ 82.812582] [<ffffffff810c84ac>] print_circular_bug+0x1fc/0x310
[ 82.812586] [<ffffffff810cbe59>] __lock_acquire+0x1fc9/0x20f0
[ 82.812590] [<ffffffff810cc883>] lock_acquire+0xc3/0x1d0
[ 82.812594] [<ffffffff8150d9c1>] ? drm_gem_mmap+0x1a1/0x270
[ 82.812599] [<ffffffff8150d9e7>] drm_gem_mmap+0x1c7/0x270
[ 82.812603] [<ffffffff8150d9c1>] ? drm_gem_mmap+0x1a1/0x270
[ 82.812608] [<ffffffff81196a14>] mmap_region+0x334/0x580
[ 82.812612] [<ffffffff81196fc4>] do_mmap+0x364/0x410
[ 82.812616] [<ffffffff8117b38d>] vm_mmap_pgoff+0x6d/0xa0
[ 82.812629] [<ffffffff811950f4>] SyS_mmap_pgoff+0x184/0x220
[ 82.812633] [<ffffffff8100a0fd>] SyS_mmap+0x1d/0x20
[ 82.812637] [<ffffffff817bb81b>] entry_SYSCALL_64_fastpath+0x16/0x73
Highly unlikely though this scenario is, we can avoid the issue entirely
by moving the copy operation from out under the kernfs_get_active()
tracking by assigning the preallocated buffer its own mutex. The
temporary buffer allocation doesn't require mutex locking as it is
entirely local.
The locked section was extended by the addition of the preallocated buf
to speed up md user operations in
commit 2b75869bba676c248d8d25ae6d2bd9221dfffdb6
Author: NeilBrown <neilb@suse.de>
Date: Mon Oct 13 16:41:28 2014 +1100
sysfs/kernfs: allow attributes to request write buffer be pre-allocated.
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94350
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: NeilBrown <neilb@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 7247252..e157400 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -190,15 +190,16 @@
char *buf;
buf = of->prealloc_buf;
- if (!buf)
+ if (buf)
+ mutex_lock(&of->prealloc_mutex);
+ else
buf = kmalloc(len, GFP_KERNEL);
if (!buf)
return -ENOMEM;
/*
* @of->mutex nests outside active ref and is used both to ensure that
- * the ops aren't called concurrently for the same open file, and
- * to provide exclusive access to ->prealloc_buf (when that exists).
+ * the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
@@ -214,21 +215,23 @@
else
len = -EINVAL;
+ kernfs_put_active(of->kn);
+ mutex_unlock(&of->mutex);
+
if (len < 0)
- goto out_unlock;
+ goto out_free;
if (copy_to_user(user_buf, buf, len)) {
len = -EFAULT;
- goto out_unlock;
+ goto out_free;
}
*ppos += len;
- out_unlock:
- kernfs_put_active(of->kn);
- mutex_unlock(&of->mutex);
out_free:
- if (buf != of->prealloc_buf)
+ if (buf == of->prealloc_buf)
+ mutex_unlock(&of->prealloc_mutex);
+ else
kfree(buf);
return len;
}
@@ -284,15 +287,22 @@
}
buf = of->prealloc_buf;
- if (!buf)
+ if (buf)
+ mutex_lock(&of->prealloc_mutex);
+ else
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
+ if (copy_from_user(buf, user_buf, len)) {
+ len = -EFAULT;
+ goto out_free;
+ }
+ buf[len] = '\0'; /* guarantee string termination */
+
/*
* @of->mutex nests outside active ref and is used both to ensure that
- * the ops aren't called concurrently for the same open file, and
- * to provide exclusive access to ->prealloc_buf (when that exists).
+ * the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
@@ -301,26 +311,22 @@
goto out_free;
}
- if (copy_from_user(buf, user_buf, len)) {
- len = -EFAULT;
- goto out_unlock;
- }
- buf[len] = '\0'; /* guarantee string termination */
-
ops = kernfs_ops(of->kn);
if (ops->write)
len = ops->write(of, buf, len, *ppos);
else
len = -EINVAL;
+ kernfs_put_active(of->kn);
+ mutex_unlock(&of->mutex);
+
if (len > 0)
*ppos += len;
-out_unlock:
- kernfs_put_active(of->kn);
- mutex_unlock(&of->mutex);
out_free:
- if (buf != of->prealloc_buf)
+ if (buf == of->prealloc_buf)
+ mutex_unlock(&of->prealloc_mutex);
+ else
kfree(buf);
return len;
}
@@ -687,6 +693,7 @@
error = -ENOMEM;
if (!of->prealloc_buf)
goto err_free;
+ mutex_init(&of->prealloc_mutex);
}
/*
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index c06c442..d306e28 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -177,6 +177,7 @@
/* private fields, do not use outside kernfs proper */
struct mutex mutex;
+ struct mutex prealloc_mutex;
int event;
struct list_head list;
char *prealloc_buf;