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SubjectRe: [f2fs-dev] [PATCH] f2fs: do not use mutex lock in atomic context
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On 2019/2/15 12:28, Ritesh Harjani wrote:
>
> On 2/14/2019 9:40 PM, Chao Yu wrote:
>> On 2019-2-14 15:46, Sahitya Tummala wrote:
>>> On Wed, Feb 13, 2019 at 11:25:31AM +0800, Chao Yu wrote:
>>>> On 2019/2/4 16:06, Sahitya Tummala wrote:
>>>>> Fix below warning coming because of using mutex lock in atomic context.
>>>>>
>>>>> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:98
>>>>> in_atomic(): 1, irqs_disabled(): 0, pid: 585, name: sh
>>>>> Preemption disabled at: __radix_tree_preload+0x28/0x130
>>>>> Call trace:
>>>>> dump_backtrace+0x0/0x2b4
>>>>> show_stack+0x20/0x28
>>>>> dump_stack+0xa8/0xe0
>>>>> ___might_sleep+0x144/0x194
>>>>> __might_sleep+0x58/0x8c
>>>>> mutex_lock+0x2c/0x48
>>>>> f2fs_trace_pid+0x88/0x14c
>>>>> f2fs_set_node_page_dirty+0xd0/0x184
>>>>>
>>>>> Do not use f2fs_radix_tree_insert() to avoid doing cond_resched() with
>>>>> spin_lock() acquired.
>>>>>
>>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>>>> ---
>>>>> fs/f2fs/trace.c | 20 +++++++++++++-------
>>>>> 1 file changed, 13 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/trace.c b/fs/f2fs/trace.c
>>>>> index ce2a5eb..d0ab533 100644
>>>>> --- a/fs/f2fs/trace.c
>>>>> +++ b/fs/f2fs/trace.c
>>>>> @@ -14,7 +14,7 @@
>>>>> #include "trace.h"
>>>>>
>>>>> static RADIX_TREE(pids, GFP_ATOMIC);
>>>>> -static struct mutex pids_lock;
>>>>> +static spinlock_t pids_lock;
>>>>> static struct last_io_info last_io;
>>>>>
>>>>> static inline void __print_last_io(void)
>>>>> @@ -58,23 +58,29 @@ void f2fs_trace_pid(struct page *page)
>>>>>
>>>>> set_page_private(page, (unsigned long)pid);
>>>>>
>>>>> +retry:
>>>>> if (radix_tree_preload(GFP_NOFS))
>>>>> return;
>>>>>
>>>>> - mutex_lock(&pids_lock);
>>>>> + spin_lock(&pids_lock);
>>>>> p = radix_tree_lookup(&pids, pid);
>>>>> if (p == current)
>>>>> goto out;
>>>>> if (p)
>>>>> radix_tree_delete(&pids, pid);
>>>>>
>>>>> - f2fs_radix_tree_insert(&pids, pid, current);
>
> Do you know why do we have a retry logic here? When anyways we have
> called for radix_tree_delete with pid key?
> Which should ensure the slot is empty, no?
> Then why in the original code (f2fs_radix_tree_insert), we were
> retrying. For what condition a retry was needed?

Hi,

f2fs_radix_tree_insert is used in many places, it was introduced to used in
some paths we should not failed.

And here, I guess we used it for the same purpose, if we failed to insert
@current pointer into radix, next time, we may not skip calling
trace_printk, actually it will print the same current->comm info as
previous one, it's redundant.

Thanks,

>
> Regards
> Ritesh
>
>
>>>>> + if (radix_tree_insert(&pids, pid, current)) {
>>>>> + spin_unlock(&pids_lock);
>>>>> + radix_tree_preload_end();
>>>>> + cond_resched();
>>>>> + goto retry;
>>>>> + }
>>>>>
>>>>> trace_printk("%3x:%3x %4x %-16s\n",
>>>>> MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
>>>>> pid, current->comm);
>>>> Hi Sahitya,
>>>>
>>>> Can trace_printk sleep? For safety, how about moving it out of spinlock?
>>>>
>>> Hi Chao,
>>>
>>> Yes, trace_printk() is safe to use in atomic context (unlike printk).
>> Hi Sahitya,
>>
>> Thanks for your confirmation. :)
>>
>> Reviewed-by: Chao Yu <yuchao0@huawei.com>
>>
>> Thanks,
>>
>>> Thanks,
>>> Sahitya.
>>>
>>>> Thanks,
>>>>
>>>>> out:
>>>>> - mutex_unlock(&pids_lock);
>>>>> + spin_unlock(&pids_lock);
>>>>> radix_tree_preload_end();
>>>>> }
>>>>>
>>>>> @@ -119,7 +125,7 @@ void f2fs_trace_ios(struct f2fs_io_info *fio, int flush)
>>>>>
>>>>> void f2fs_build_trace_ios(void)
>>>>> {
>>>>> - mutex_init(&pids_lock);
>>>>> + spin_lock_init(&pids_lock);
>>>>> }
>>>>>
>>>>> #define PIDVEC_SIZE 128
>>>>> @@ -147,7 +153,7 @@ void f2fs_destroy_trace_ios(void)
>>>>> pid_t next_pid = 0;
>>>>> unsigned int found;
>>>>>
>>>>> - mutex_lock(&pids_lock);
>>>>> + spin_lock(&pids_lock);
>>>>> while ((found = gang_lookup_pids(pid, next_pid, PIDVEC_SIZE))) {
>>>>> unsigned idx;
>>>>>
>>>>> @@ -155,5 +161,5 @@ void f2fs_destroy_trace_ios(void)
>>>>> for (idx = 0; idx < found; idx++)
>>>>> radix_tree_delete(&pids, pid[idx]);
>>>>> }
>>>>> - mutex_unlock(&pids_lock);
>>>>> + spin_unlock(&pids_lock);
>>>>> }
>>>>>
>>
>> _______________________________________________
>> Linux-f2fs-devel mailing list
>> Linux-f2fs-devel@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>
> .
>

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