linux-kernel - Re: [PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c

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Message-ID: <7815A35E-6506-477D-8E57-3960F7C1FE62@fb.com>
Date:   Tue, 22 May 2018 21:56:18 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] perf/core: fix bad use of igrab in
 kernel/event/core.c


> On Apr 18, 2018, at 11:17 PM, Alexander Shishkin <alexander.shishkin@...ux.intel.com> wrote:
> 
> On Tue, Apr 17, 2018 at 11:29:07PM -0700, Song Liu wrote:
>> As Miklos reported and suggested:
>> 
>>  This pattern repeats two times in trace_uprobe.c and in
>>  kernel/events/core.c as well:
>> 
>>      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>      if (ret)
>>          goto fail_address_parse;
>> 
>>      inode = igrab(d_inode(path.dentry));
>>      path_put(&path);
>> 
>>  And it's wrong.  You can only hold a reference to the inode if you
>>  have an active ref to the superblock as well (which is normally
>>  through path.mnt) or holding s_umount.
> 
> Oops. I must have snatched it from the uprobe code without thinking.
> 
>>  This way unmounting the containing filesystem while the tracepoint is
>>  active will give you the "VFS: Busy inodes after unmount..." message
>>  and a crash when the inode is finally put.
>> 
>>  Solution: store path instead of inode.
>> 
>> This patch fixes the issue in kernel/event/core.c.
>> 
>> NOTE: Based on my understanding, perf_addr_filter only supports intel_pt.
> 
> Coresight too, but that's probably even further away from what you have.
> 
>> However, my test system doesn't support address filtering (or I made a
>> mistake?). Therefore, I have NOT tested this patch.
> 
> Check /sys/devices/intel_pt/caps/num_address_ranges, if it's non-zero,
> it's supported.
> 
>> Could someone please help test it?
> 
> Yes:
> 
> Reviewed-and-tested-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> 
> The subject line needs a little love to be more like other perf commits, but
> other than that, looks good.
> 
> Thanks!

Did this patch ever make into tip/perf/XX trees? If not, what shall I do 
to move it ahead?

Thanks,
Song