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SubjectRe: [PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c
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@linux.intel.com>

The subject line needs a little love to be more like other perf commits, but
other than that, looks good.

Thanks!

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