Messages in this thread | | | Date | Fri, 20 May 2022 08:29:18 +0200 | Subject | Re: [RFC PATCH] procfs: Add file path and size to /proc/<pid>/fdinfo | From | Christian König <> |
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Am 19.05.22 um 23:40 schrieb Kalesh Singh: > Processes can pin shared memory by keeping a handle to it through a > file descriptor; for instance dmabufs, memfd, and ashsmem (in Android). > > In the case of a memory leak, to identify the process pinning the > memory, userspace needs to: > - Iterate the /proc/<pid>/fd/* for each process > - Do a readlink on each entry to identify the type of memory from > the file path. > - stat() each entry to get the size of the memory. > > The file permissions on /proc/<pid>/fd/* only allows for the owner > or root to perform the operations above; and so is not suitable for > capturing the system-wide state in a production environment. > > This issue was addressed for dmabufs by making /proc/*/fdinfo/* > accessible to a process with PTRACE_MODE_READ_FSCREDS credentials[1] > To allow the same kind of tracking for other types of shared memory, > add the following fields to /proc/<pid>/fdinfo/<fd>: > > path - This allows identifying the type of memory based on common > prefixes: e.g. "/memfd...", "/dmabuf...", "/dev/ashmem..." > > This was not an issued when dmabuf tracking was introduced > because the exp_name field of dmabuf fdinfo could be used > to distinguish dmabuf fds from other types. > > size - To track the amount of memory that is being pinned. > > dmabufs expose size as an additional field in fdinfo. Remove > this and make it a common field for all fds. > > Access to /proc/<pid>/fdinfo is governed by PTRACE_MODE_READ_FSCREDS > -- the same as for /proc/<pid>/maps which also exposes the path and > size for mapped memory regions. > > This allows for a system process with PTRACE_MODE_READ_FSCREDS to > account the pinned per-process memory via fdinfo.
I think this should be split into two patches, one adding the size and one adding the path.
Adding the size is completely unproblematic, but the path might raise some eyebrows.
> > [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20210308170651.919148-1-kaleshsingh%40google.com%2F&data=05%7C01%7Cchristian.koenig%40amd.com%7C95ee7bf71c2c4aa342fa08da39e03398%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637885932392014544%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kf%2B2es12hV3z5zjOFhx3EyxI1XEMeHexqTLNpNoDhAY%3D&reserved=0 > > Signed-off-by: Kalesh Singh <kaleshsingh@google.com> > --- > Documentation/filesystems/proc.rst | 22 ++++++++++++++++++++-- > drivers/dma-buf/dma-buf.c | 1 - > fs/proc/fd.c | 9 +++++++-- > 3 files changed, 27 insertions(+), 5 deletions(-) > > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst > index 061744c436d9..ad66d78aca51 100644 > --- a/Documentation/filesystems/proc.rst > +++ b/Documentation/filesystems/proc.rst > @@ -1922,13 +1922,16 @@ if precise results are needed. > 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file > --------------------------------------------------------------- > This file provides information associated with an opened file. The regular > -files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. > +files have at least six fields -- 'pos', 'flags', 'mnt_id', 'ino', 'size', > +and 'path'. > + > The 'pos' represents the current offset of the opened file in decimal > form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the > file has been created with [see open(2) for details] and 'mnt_id' represents > mount ID of the file system containing the opened file [see 3.5 > /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of > -the file. > +the file, 'size' represents the size of the file in bytes, and 'path' > +represents the file path. > > A typical output is:: > > @@ -1936,6 +1939,8 @@ A typical output is:: > flags: 0100002 > mnt_id: 19 > ino: 63107 > + size: 0 > + path: /dev/null > > All locks associated with a file descriptor are shown in its fdinfo too:: > > @@ -1953,6 +1958,8 @@ Eventfd files > flags: 04002 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:[eventfd] > eventfd-count: 5a > > where 'eventfd-count' is hex value of a counter. > @@ -1966,6 +1973,8 @@ Signalfd files > flags: 04002 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:[signalfd] > sigmask: 0000000000000200 > > where 'sigmask' is hex value of the signal mask associated > @@ -1980,6 +1989,8 @@ Epoll files > flags: 02 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:[eventpoll] > tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 > > where 'tfd' is a target file descriptor number in decimal form, > @@ -1998,6 +2009,8 @@ For inotify files the format is the following:: > flags: 02000000 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:inotify > inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d > > where 'wd' is a watch descriptor in decimal form, i.e. a target file > @@ -2021,6 +2034,8 @@ For fanotify files the format is:: > flags: 02 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:[fanotify] > fanotify flags:10 event-flags:0 > fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 > fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 > @@ -2046,6 +2061,8 @@ Timerfd files > flags: 02 > mnt_id: 9 > ino: 63107 > + size: 0 > + path: anon_inode:[timerfd] > clockid: 0 > ticks: 0 > settime flags: 01 > @@ -2070,6 +2087,7 @@ DMA Buffer files > mnt_id: 9 > ino: 63107 > size: 32768 > + path: /dmabuf: > count: 2 > exp_name: system-heap > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index b1e25ae98302..d61183ff3c30 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -377,7 +377,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) > { > struct dma_buf *dmabuf = file->private_data; > > - seq_printf(m, "size:\t%zu\n", dmabuf->size); > /* Don't count the temporary reference taken inside procfs seq_show */ > seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1); > seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name); > diff --git a/fs/proc/fd.c b/fs/proc/fd.c > index 913bef0d2a36..a8a968bc58f0 100644 > --- a/fs/proc/fd.c > +++ b/fs/proc/fd.c > @@ -54,10 +54,15 @@ static int seq_show(struct seq_file *m, void *v) > if (ret) > return ret; > > - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n", > + seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\nsize:\t%zu\n", > (long long)file->f_pos, f_flags, > real_mount(file->f_path.mnt)->mnt_id, > - file_inode(file)->i_ino); > + file_inode(file)->i_ino, > + file_inode(file)->i_size);
We might consider splitting this into multiple seq_printf calls, one for each printed attribute.
It becomes a bit unreadable and the minimal additional overhead shouldn't matter that much.
Regards, Christian.
> + > + seq_puts(m, "path:\t"); > + seq_file_path(m, file, "\n"); > + seq_putc(m, '\n'); > > /* show_fd_locks() never deferences files so a stale value is safe */ > show_fd_locks(m, file, files); > > base-commit: b015dcd62b86d298829990f8261d5d154b8d7af5
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