Messages in this thread | | | Date | Wed, 2 Oct 2013 19:46:39 +0400 | From | Maxim Patlasov <> | Subject | Re: [PATCH 2/5] fuse: writepages: crop secondary requests on send -v2 |
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On 10/02/2013 07:07 PM, Miklos Szeredi wrote: > On Wed, Oct 2, 2013 at 1:17 PM, Maxim Patlasov <MPatlasov@parallels.com> wrote: >> If writeback happens while fuse is in FUSE_NOWRITE condition, the request >> will be queued but not processed immediately (see fuse_flush_writepages()). >> Until FUSE_NOWRITE becomes relaxed, more writebacks can happen. They will >> be queued as "secondary" requests to that first ("primary") request. >> >> When FUSE_NOWRITE is relaxed and fuse_send_writepage() is called, it must >> crop both primary and secondary requests according to the actual i_size. >> Otherwise, if only primary is cropped, an extending write(2) may increase >> i_size soon and then secondary requests won't be cropped properly. The result >> would be stale data written to the server to a file offset where zeros must be. >> >> Changed in v2: >> - avoid NULL pointer dereference in fuse_drop_writepage(). >> >> Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com> >> --- >> fs/fuse/file.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++-------- >> 1 file changed, 55 insertions(+), 9 deletions(-) >> >> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >> index 575e44f..89a2e76 100644 >> --- a/fs/fuse/file.c >> +++ b/fs/fuse/file.c >> @@ -1435,6 +1435,51 @@ static void fuse_writepage_finish(struct fuse_conn *fc, struct fuse_req *req) >> wake_up(&fi->page_waitq); >> } >> >> +/* Drop list of secondary writepage requests */ >> +static void fuse_drop_writepage(struct fuse_conn *fc, struct fuse_req *req) >> +{ >> + struct backing_dev_info *bdi = req ? >> + req->inode->i_mapping->backing_dev_info : NULL; >> + >> + while (req) { >> + struct fuse_req *next = req->misc.write.next; >> + dec_bdi_stat(bdi, BDI_WRITEBACK); >> + dec_zone_page_state(req->pages[0], NR_WRITEBACK_TEMP); >> + fuse_writepage_free(fc, req); >> + fuse_put_request(fc, req); >> + req = next; >> + } >> +} >> + >> +/* Crop the misc.write.in.size of parent and secondary writepage requests */ >> +static bool fuse_crop_writepage(struct fuse_conn *fc, struct fuse_req *req, >> + loff_t size, struct fuse_req **drop_list) >> +{ >> + if (req->misc.write.in.offset >= size) >> + return true; >> + >> + while (req) { >> + struct fuse_req *next = req->misc.write.next; >> + struct fuse_write_in *inarg = &req->misc.write.in; >> + __u64 data_size = inarg->size ? : >> + req->num_pages * PAGE_CACHE_SIZE; >> + >> + if (inarg->offset + data_size <= size) { >> + inarg->size = data_size; >> + } else if (inarg->offset < size) { >> + inarg->size = size - inarg->offset; >> + } else { >> + /* Got truncated off completely */ >> + req->misc.write.next = *drop_list; >> + *drop_list = req; > This corrupts the list (the req is not taken off the list before being > added to another). It could be fixed, but why not check this instead > in fuse_writepage_end() before queuing the next request?
Nice idea. This will make next patch ("crop on attach") redundant. I'll resend updated patch-set.
Thanks, Maxim
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