From: Nick Piggin Date: Fri, 12 Sep 2008 09:24:11 +0000 (+0200) Subject: sysfs: fix deadlock X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b31ca3f5dfc;p=linux-beck.git sysfs: fix deadlock On Thu, Sep 11, 2008 at 10:27:10AM +0200, Ingo Molnar wrote: > and it's working fine on most boxes. One testbox found this new locking > scenario: > > PM: Adding info for No Bus:vcsa7 > EDAC DEBUG: MC0: i82860_check() > > ======================================================= > [ INFO: possible circular locking dependency detected ] > 2.6.27-rc6-tip #1 > ------------------------------------------------------- > X/4873 is trying to acquire lock: > (&bb->mutex){--..}, at: [] mmap+0x40/0xa0 > > but task is already holding lock: > (&mm->mmap_sem){----}, at: [] sys_mmap2+0x8e/0xc0 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (&mm->mmap_sem){----}: > [] validate_chain+0xa96/0xf50 > [] __lock_acquire+0x2cb/0x5b0 > [] lock_acquire+0x89/0xc0 > [] might_fault+0x6b/0x90 > [] copy_to_user+0x38/0x60 > [] read+0xfb/0x170 > [] vfs_read+0x95/0x110 > [] sys_pread64+0x63/0x80 > [] sysenter_do_call+0x12/0x43 > [] 0xffffffff > > -> #0 (&bb->mutex){--..}: > [] validate_chain+0x6b7/0xf50 > [] __lock_acquire+0x2cb/0x5b0 > [] lock_acquire+0x89/0xc0 > [] __mutex_lock_common+0xab/0x3c0 > [] mutex_lock_nested+0x38/0x50 > [] mmap+0x40/0xa0 > [] mmap_region+0x14e/0x450 > [] do_mmap_pgoff+0x2ef/0x310 > [] sys_mmap2+0xad/0xc0 > [] sysenter_do_call+0x12/0x43 > [] 0xffffffff > > other info that might help us debug this: > > 1 lock held by X/4873: > #0: (&mm->mmap_sem){----}, at: [] sys_mmap2+0x8e/0xc0 > > stack backtrace: > Pid: 4873, comm: X Not tainted 2.6.27-rc6-tip #1 > [] print_circular_bug_tail+0x79/0xc0 > [] validate_chain+0x6b7/0xf50 > [] ? trace_hardirqs_off_caller+0x15/0xb0 > [] __lock_acquire+0x2cb/0x5b0 > [] lock_acquire+0x89/0xc0 > [] ? mmap+0x40/0xa0 > [] __mutex_lock_common+0xab/0x3c0 > [] ? mmap+0x40/0xa0 > [] mutex_lock_nested+0x38/0x50 > [] ? mmap+0x40/0xa0 > [] mmap+0x40/0xa0 > [] mmap_region+0x14e/0x450 > [] ? arch_get_unmapped_area_topdown+0xf8/0x160 > [] do_mmap_pgoff+0x2ef/0x310 > [] sys_mmap2+0xad/0xc0 > [] sysenter_do_call+0x12/0x43 > [] ? __switch_to+0x130/0x220 > ======================= > evbug.c: Event. Dev: input3, Type: 20, Code: 0, Value: 500 > warning: `sudo' uses deprecated v2 capabilities in a way that may be insecure. > > i've attached the config. > > at first sight it looks like a genuine bug in fs/sysfs/bin.c? Yes, it is a real bug by the looks. bin.c takes bb->mutex under mmap_sem when it is mmapped, and then does its copy_*_user under bb->mutex too. Here is a basic fix for the sysfs lor. From: Nick Piggin Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/sysfs/bin.c b/fs/sysfs/bin.c index 006fc64227dd..66f6e58a7e4b 100644 --- a/fs/sysfs/bin.c +++ b/fs/sysfs/bin.c @@ -61,6 +61,7 @@ read(struct file *file, char __user *userbuf, size_t bytes, loff_t *off) int size = dentry->d_inode->i_size; loff_t offs = *off; int count = min_t(size_t, bytes, PAGE_SIZE); + char *temp; if (size) { if (offs > size) @@ -69,23 +70,33 @@ read(struct file *file, char __user *userbuf, size_t bytes, loff_t *off) count = size - offs; } + temp = kmalloc(count, GFP_KERNEL); + if (!temp) + return -ENOMEM; + mutex_lock(&bb->mutex); count = fill_read(dentry, bb->buffer, offs, count); - if (count < 0) - goto out_unlock; + if (count < 0) { + mutex_unlock(&bb->mutex); + goto out_free; + } - if (copy_to_user(userbuf, bb->buffer, count)) { + memcpy(temp, bb->buffer, count); + + mutex_unlock(&bb->mutex); + + if (copy_to_user(userbuf, temp, count)) { count = -EFAULT; - goto out_unlock; + goto out_free; } pr_debug("offs = %lld, *off = %lld, count = %d\n", offs, *off, count); *off = offs + count; - out_unlock: - mutex_unlock(&bb->mutex); + out_free: + kfree(temp); return count; } @@ -118,6 +129,7 @@ static ssize_t write(struct file *file, const char __user *userbuf, int size = dentry->d_inode->i_size; loff_t offs = *off; int count = min_t(size_t, bytes, PAGE_SIZE); + char *temp; if (size) { if (offs > size) @@ -126,19 +138,27 @@ static ssize_t write(struct file *file, const char __user *userbuf, count = size - offs; } - mutex_lock(&bb->mutex); + temp = kmalloc(count, GFP_KERNEL); + if (!temp) + return -ENOMEM; - if (copy_from_user(bb->buffer, userbuf, count)) { + if (copy_from_user(temp, userbuf, count)) { count = -EFAULT; - goto out_unlock; + goto out_free; } + mutex_lock(&bb->mutex); + + memcpy(bb->buffer, temp, count); + count = flush_write(dentry, bb->buffer, offs, count); + mutex_unlock(&bb->mutex); + if (count > 0) *off = offs + count; - out_unlock: - mutex_unlock(&bb->mutex); +out_free: + kfree(temp); return count; }