# git rev-parse -q --verify 2be7d348fe924f0c5583c6a805bd42cecda93104^{commit} 2be7d348fe924f0c5583c6a805bd42cecda93104 already have revision, skipping fetch # git checkout -q -f -B kisskb 2be7d348fe924f0c5583c6a805bd42cecda93104 # git clean -qxdf # < git log -1 # commit 2be7d348fe924f0c5583c6a805bd42cecda93104 # Author: Linus Torvalds # Date: Tue Nov 26 11:34:06 2019 -0800 # # Revert "vfs: properly and reliably lock f_pos in fdget_pos()" # # This reverts commit 0be0ee71816b2b6725e2b4f32ad6726c9d729777. # # I was hoping it would be benign to switch over entirely to FMODE_STREAM, # and we'd have just a couple of small fixups we'd need, but it looks like # we're not quite there yet. # # While it worked fine on both my desktop and laptop, they are fairly # similar in other respects, and run mostly the same loads. Kenneth # Crudup reports that it seems to break both his vmware installation and # the KDE upower service. In both cases apparently leading to timeouts # due to waitinmg for the f_pos lock. # # There are a number of character devices in particular that definitely # want stream-like behavior, but that currently don't get marked as # streams, and as a result get the exclusion between concurrent # read()/write() on the same file descriptor. Which doesn't work well for # them. # # The most obvious example if this is /dev/console and /dev/tty, which use # console_fops and tty_fops respectively (and ptmx_fops for the pty master # side). It may be that it's just this that causes problems, but we # clearly weren't ready yet. # # Because there's a number of other likely common cases that don't have # llseek implementations and would seem to act as stream devices: # # /dev/fuse (fuse_dev_operations) # /dev/mcelog (mce_chrdev_ops) # /dev/mei0 (mei_fops) # /dev/net/tun (tun_fops) # /dev/nvme0 (nvme_dev_fops) # /dev/tpm0 (tpm_fops) # /proc/self/ns/mnt (ns_file_operations) # /dev/snd/pcm* (snd_pcm_f_ops[]) # # and while some of these could be trivially automatically detected by the # vfs layer when the character device is opened by just noticing that they # have no read or write operations either, it often isn't that obvious. # # Some character devices most definitely do use the file position, even if # they don't allow seeking: the firmware update code, for example, uses # simple_read_from_buffer() that does use f_pos, but doesn't allow seeking # back and forth. # # We'll revisit this when there's a better way to detect the problem and # fix it (possibly with a coccinelle script to do more of the FMODE_STREAM # annotations). # # Reported-by: Kenneth R. Crudup # Cc: Kirill Smelkov # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa64-linux/bin/hppa64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa64-linux/bin/hppa64-linux-ld --version # < git log --format=%s --max-count=1 2be7d348fe924f0c5583c6a805bd42cecda93104 # < make -s -j 10 ARCH=parisc O=/kisskb/build/linus_a500_defconfig_parisc64 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa64-linux/bin/hppa64-linux- a500_defconfig # make -s -j 10 ARCH=parisc O=/kisskb/build/linus_a500_defconfig_parisc64 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa64-linux/bin/hppa64-linux- In file included from /kisskb/src/arch/parisc/include/asm/atomic.h:10, from /kisskb/src/include/linux/atomic.h:7, from /kisskb/src/arch/parisc/include/asm/bitops.h:13, from /kisskb/src/include/linux/bitops.h:26, from /kisskb/src/include/linux/kernel.h:12, from /kisskb/src/include/linux/list.h:9, from /kisskb/src/include/linux/preempt.h:11, from /kisskb/src/include/linux/spinlock.h:51, from /kisskb/src/include/linux/seqlock.h:36, from /kisskb/src/include/linux/time.h:6, from /kisskb/src/fs/nfs/read.c:11: /kisskb/src/fs/nfs/read.c: In function 'nfs_read_completion': /kisskb/src/arch/parisc/include/asm/cmpxchg.h:48:3: warning: value computed is not used [-Wunused-value] ((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))) ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /kisskb/src/fs/nfs/read.c:196:5: note: in expansion of macro 'xchg' xchg(&nfs_req_openctx(req)->error, error); ^~~~ /kisskb/src/fs/nfs/read.c: In function 'nfs_readpage': /kisskb/src/arch/parisc/include/asm/cmpxchg.h:48:3: warning: value computed is not used [-Wunused-value] ((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))) ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /kisskb/src/fs/nfs/read.c:352:2: note: in expansion of macro 'xchg' xchg(&ctx->error, 0); ^~~~ In file included from /kisskb/src/arch/parisc/include/asm/atomic.h:10, from /kisskb/src/include/linux/atomic.h:7, from /kisskb/src/arch/parisc/include/asm/bitops.h:13, from /kisskb/src/include/linux/bitops.h:26, from /kisskb/src/include/linux/kernel.h:12, from /kisskb/src/include/linux/list.h:9, from /kisskb/src/include/linux/module.h:9, from /kisskb/src/drivers/scsi/scsi_debug.c:18: /kisskb/src/drivers/scsi/scsi_debug.c: In function 'resp_start_stop': /kisskb/src/arch/parisc/include/asm/cmpxchg.h:48:3: warning: value computed is not used [-Wunused-value] ((__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))) /kisskb/src/arch/parisc/include/asm/atomic.h:78:30: note: in expansion of macro 'xchg' #define atomic_xchg(v, new) (xchg(&((v)->counter), new)) ^~~~ /kisskb/src/drivers/scsi/scsi_debug.c:1618:2: note: in expansion of macro 'atomic_xchg' atomic_xchg(&devip->stopped, stop); ^~~~~~~~~~~ Completed OK # rm -rf /kisskb/build/linus_a500_defconfig_parisc64 # Build took: 0:02:35.974019