Author: asomers Date: Sun Sep 27 02:59:28 2020 New Revision: 366190 URL: https://svnweb.freebsd.org/changeset/base/366190
Log: MFC r366121: fusefs: fix mmap'd writes in direct_io mode If a FUSE server returns FOPEN_DIRECT_IO in response to FUSE_OPEN, that instructs the kernel to bypass the page cache for that file. This feature is also known by libfuse's name: "direct_io". However, when accessing a file via mmap, there is no possible way to bypass the cache completely. This change fixes a deadlock that would happen when an mmap'd write tried to invalidate a portion of the cache, wrongly assuming that a write couldn't possibly come from cache if direct_io were set. Arguably, we could instead disable mmap for files with FOPEN_DIRECT_IO set. But allowing it is less likely to cause user complaints, and is more in keeping with the spirit of open(2), where O_DIRECT instructs the kernel to "reduce", not "eliminate" cache effects. PR: 247276 Reported by: trape...@spawn.link Reviewed by: cem Differential Revision: https://reviews.freebsd.org/D26485 Modified: stable/12/sys/fs/fuse/fuse_io.c stable/12/tests/sys/fs/fusefs/write.cc Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/fs/fuse/fuse_io.c ============================================================================== --- stable/12/sys/fs/fuse/fuse_io.c Sat Sep 26 23:05:38 2020 (r366189) +++ stable/12/sys/fs/fuse/fuse_io.c Sun Sep 27 02:59:28 2020 (r366190) @@ -291,6 +291,7 @@ fuse_io_dispatch(struct vnode *vp, struct uio *uio, in fuse_vnode_update(vp, FN_MTIMECHANGE | FN_CTIMECHANGE); if (directio) { off_t start, end, filesize; + bool pages = (ioflag & IO_VMIO) != 0; SDT_PROBE2(fusefs, , io, trace, 1, "direct write of vnode"); @@ -301,15 +302,14 @@ fuse_io_dispatch(struct vnode *vp, struct uio *uio, in start = uio->uio_offset; end = start + uio->uio_resid; - KASSERT((ioflag & (IO_VMIO | IO_DIRECT)) != - (IO_VMIO | IO_DIRECT), - ("IO_DIRECT used for a cache flush?")); - /* Invalidate the write cache when writing directly */ - err = fuse_inval_buf_range(vp, filesize, start, end); - if (err) - return (err); + if (!pages) { + err = fuse_inval_buf_range(vp, filesize, start, + end); + if (err) + return (err); + } err = fuse_write_directbackend(vp, uio, cred, fufh, - filesize, ioflag, false); + filesize, ioflag, pages); } else { SDT_PROBE2(fusefs, , io, trace, 1, "buffered write of vnode"); Modified: stable/12/tests/sys/fs/fusefs/write.cc ============================================================================== --- stable/12/tests/sys/fs/fusefs/write.cc Sat Sep 26 23:05:38 2020 (r366189) +++ stable/12/tests/sys/fs/fusefs/write.cc Sun Sep 27 02:59:28 2020 (r366190) @@ -923,6 +923,76 @@ TEST_F(WriteBack, o_direct) leak(fd); } +TEST_F(WriteBack, direct_io) +{ + const char FULLPATH[] = "mountpoint/some_file.txt"; + const char RELPATH[] = "some_file.txt"; + const char *CONTENTS = "abcdefgh"; + uint64_t ino = 42; + int fd; + ssize_t bufsize = strlen(CONTENTS); + uint8_t readbuf[bufsize]; + + expect_lookup(RELPATH, ino, 0); + expect_open(ino, FOPEN_DIRECT_IO, 1); + FuseTest::expect_write(ino, 0, bufsize, bufsize, 0, FUSE_WRITE_CACHE, + CONTENTS); + expect_read(ino, 0, bufsize, bufsize, CONTENTS); + + fd = open(FULLPATH, O_RDWR); + EXPECT_LE(0, fd) << strerror(errno); + + ASSERT_EQ(bufsize, write(fd, CONTENTS, bufsize)) << strerror(errno); + /* A subsequent read must query the daemon because cache is empty */ + ASSERT_EQ(0, lseek(fd, 0, SEEK_SET)) << strerror(errno); + ASSERT_EQ(0, fcntl(fd, F_SETFL, 0)) << strerror(errno); + ASSERT_EQ(bufsize, read(fd, readbuf, bufsize)) << strerror(errno); + leak(fd); +} + +/* + * mmap should still be possible even if the server used direct_io. Mmap will + * still use the cache, though. + * + * Regression test for bug 247276 + * https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247276 + */ +TEST_F(WriteBack, mmap_direct_io) +{ + const char FULLPATH[] = "mountpoint/some_file.txt"; + const char RELPATH[] = "some_file.txt"; + const char *CONTENTS = "abcdefgh"; + uint64_t ino = 42; + int fd; + size_t len; + ssize_t bufsize = strlen(CONTENTS); + void *p, *zeros; + + len = getpagesize(); + zeros = calloc(1, len); + ASSERT_NE(nullptr, zeros); + + expect_lookup(RELPATH, ino, len); + expect_open(ino, FOPEN_DIRECT_IO, 1); + expect_read(ino, 0, len, len, zeros); + expect_flush(ino, 1, ReturnErrno(0)); + FuseTest::expect_write(ino, 0, len, len, FUSE_WRITE_CACHE, 0, zeros); + expect_release(ino, ReturnErrno(0)); + + fd = open(FULLPATH, O_RDWR); + EXPECT_LE(0, fd) << strerror(errno); + + p = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + ASSERT_NE(MAP_FAILED, p) << strerror(errno); + + memmove((uint8_t*)p, CONTENTS, bufsize); + + ASSERT_EQ(0, munmap(p, len)) << strerror(errno); + close(fd); // Write mmap'd data on close + + free(zeros); +} + /* * When mounted with -o async, the writeback cache mode should delay writes */ _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
