diff options
| author | Kirill Smelkov <kirr@nexedi.com> | 2019-03-27 10:15:19 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-06-22 08:17:15 +0200 |
| commit | 4edf907dcd42d1d5790b54db472d08ee67c348a2 (patch) | |
| tree | 7ff7100d531325348c57d83064632c226835e082 /fs/fuse | |
| parent | faa4dc52b4b227344bd66ac0fda6475749263d8b (diff) | |
fuse: retrieve: cap requested size to negotiated max_write
[ Upstream commit 7640682e67b33cab8628729afec8ca92b851394f ]
FUSE filesystem server and kernel client negotiate during initialization
phase, what should be the maximum write size the client will ever issue.
Correspondingly the filesystem server then queues sys_read calls to read
requests with buffer capacity large enough to carry request header + that
max_write bytes. A filesystem server is free to set its max_write in
anywhere in the range between [1*page, fc->max_pages*page]. In particular
go-fuse[2] sets max_write by default as 64K, wheres default fc->max_pages
corresponds to 128K. Libfuse also allows users to configure max_write, but
by default presets it to possible maximum.
If max_write is < fc->max_pages*page, and in NOTIFY_RETRIEVE handler we
allow to retrieve more than max_write bytes, corresponding prepared
NOTIFY_REPLY will be thrown away by fuse_dev_do_read, because the
filesystem server, in full correspondence with server/client contract, will
be only queuing sys_read with ~max_write buffer capacity, and
fuse_dev_do_read throws away requests that cannot fit into server request
buffer. In turn the filesystem server could get stuck waiting indefinitely
for NOTIFY_REPLY since NOTIFY_RETRIEVE handler returned OK which is
understood by clients as that NOTIFY_REPLY was queued and will be sent
back.
Cap requested size to negotiate max_write to avoid the problem. This
aligns with the way NOTIFY_RETRIEVE handler works, which already
unconditionally caps requested retrieve size to fuse_conn->max_pages. This
way it should not hurt NOTIFY_RETRIEVE semantic if we return less data than
was originally requested.
Please see [1] for context where the problem of stuck filesystem was hit
for real, how the situation was traced and for more involving patch that
did not make it into the tree.
[1] https://marc.info/?l=linux-fsdevel&m=155057023600853&w=2
[2] https://github.com/hanwen/go-fuse
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Cc: Han-Wen Nienhuys <hanwen@google.com>
Cc: Jakob Unterwurzacher <jakobunt@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'fs/fuse')
| -rw-r--r-- | fs/fuse/dev.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index eaedbc1a3e95..8016cd059db1 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -1668,7 +1668,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode, offset = outarg->offset & ~PAGE_MASK; file_size = i_size_read(inode); - num = outarg->size; + num = min(outarg->size, fc->max_write); if (outarg->offset > file_size) num = 0; else if (outarg->offset + num > file_size) |