| Message ID | 1498744902-22754-1-git-send-email-rabin.vincent@axis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
2017-06-29 7:01 GMT-07:00 Rabin Vincent <rabin.vincent@axis.com>: > From: Rabin Vincent <rabinv@axis.com> > > When a CIFS filesystem is mounted with the forcemand option and the > following command is run on it, lockdep warns about a circular locking > dependency between CifsInodeInfo::lock_sem and the inode lock. > > while echo foo > hello; do :; done & while touch -c hello; do :; done > > cifs_writev() takes the locks in the wrong order, but note that we can't > only flip the order around because it releases the inode lock before the > call to generic_write_sync() while it holds the lock_sem across that > call. > > But, AFAICS, there is no need to hold the CifsInodeInfo::lock_sem across > the generic_write_sync() call either, so we can release both the locks > before generic_write_sync(), and change the order. > > ====================================================== > WARNING: possible circular locking dependency detected > 4.12.0-rc7+ #9 Not tainted > ------------------------------------------------------ > touch/487 is trying to acquire lock: > (&cifsi->lock_sem){++++..}, at: cifsFileInfo_put+0x88f/0x16a0 > > but task is already holding lock: > (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #1 (&sb->s_type->i_mutex_key#11){+.+.+.}: > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifs_strict_writev+0x3cb/0x8c0 > __vfs_write+0x4c1/0x930 > vfs_write+0x14c/0x2d0 > SyS_write+0xf7/0x240 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > -> #0 (&cifsi->lock_sem){++++..}: > check_prevs_add+0xfa0/0x1d10 > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifsFileInfo_put+0x88f/0x16a0 > cifs_setattr+0x992/0x1680 > notify_change+0x61a/0xa80 > utimes_common+0x3d4/0x870 > do_utimes+0x1c1/0x220 > SyS_utimensat+0x84/0x1a0 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&sb->s_type->i_mutex_key#11); > lock(&cifsi->lock_sem); > lock(&sb->s_type->i_mutex_key#11); > lock(&cifsi->lock_sem); > > *** DEADLOCK *** > > 2 locks held by touch/487: > #0: (sb_writers#10){.+.+.+}, at: mnt_want_write+0x41/0xb0 > #1: (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870 > > stack backtrace: > CPU: 0 PID: 487 Comm: touch Not tainted 4.12.0-rc7+ #9 > Call Trace: > dump_stack+0xdb/0x185 > print_circular_bug+0x45b/0x790 > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifsFileInfo_put+0x88f/0x16a0 > cifs_setattr+0x992/0x1680 > notify_change+0x61a/0xa80 > utimes_common+0x3d4/0x870 > do_utimes+0x1c1/0x220 > SyS_utimensat+0x84/0x1a0 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > Fixes: 19dfc1f5f2ef03a52 ("cifs: fix the race in cifs_writev()") > Signed-off-by: Rabin Vincent <rabinv@axis.com> > --- > fs/cifs/file.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > index fcef706..d16fa55 100644 > --- a/fs/cifs/file.c > +++ b/fs/cifs/file.c > @@ -2810,12 +2810,12 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) > struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server; > ssize_t rc; > > + inode_lock(inode); > /* > * We need to hold the sem to be sure nobody modifies lock list > * with a brlock that prevents writing. > */ > down_read(&cinode->lock_sem); > - inode_lock(inode); > > rc = generic_write_checks(iocb, from); > if (rc <= 0) > @@ -2828,11 +2828,11 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) > else > rc = -EACCES; > out: > + up_read(&cinode->lock_sem); > inode_unlock(inode); > > if (rc > 0) > rc = generic_write_sync(iocb, rc); > - up_read(&cinode->lock_sem); > return rc; > } > > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-cifs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html Acked-by: Pavel Shilovsky <pshilov@microsoft.com> -- Best regards, Pavel Shilovsky -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
merged into cifs-2.6.git for-next On Thu, Jun 29, 2017 at 9:01 AM, Rabin Vincent <rabin.vincent@axis.com> wrote: > From: Rabin Vincent <rabinv@axis.com> > > When a CIFS filesystem is mounted with the forcemand option and the > following command is run on it, lockdep warns about a circular locking > dependency between CifsInodeInfo::lock_sem and the inode lock. > > while echo foo > hello; do :; done & while touch -c hello; do :; done > > cifs_writev() takes the locks in the wrong order, but note that we can't > only flip the order around because it releases the inode lock before the > call to generic_write_sync() while it holds the lock_sem across that > call. > > But, AFAICS, there is no need to hold the CifsInodeInfo::lock_sem across > the generic_write_sync() call either, so we can release both the locks > before generic_write_sync(), and change the order. > > ====================================================== > WARNING: possible circular locking dependency detected > 4.12.0-rc7+ #9 Not tainted > ------------------------------------------------------ > touch/487 is trying to acquire lock: > (&cifsi->lock_sem){++++..}, at: cifsFileInfo_put+0x88f/0x16a0 > > but task is already holding lock: > (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #1 (&sb->s_type->i_mutex_key#11){+.+.+.}: > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifs_strict_writev+0x3cb/0x8c0 > __vfs_write+0x4c1/0x930 > vfs_write+0x14c/0x2d0 > SyS_write+0xf7/0x240 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > -> #0 (&cifsi->lock_sem){++++..}: > check_prevs_add+0xfa0/0x1d10 > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifsFileInfo_put+0x88f/0x16a0 > cifs_setattr+0x992/0x1680 > notify_change+0x61a/0xa80 > utimes_common+0x3d4/0x870 > do_utimes+0x1c1/0x220 > SyS_utimensat+0x84/0x1a0 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&sb->s_type->i_mutex_key#11); > lock(&cifsi->lock_sem); > lock(&sb->s_type->i_mutex_key#11); > lock(&cifsi->lock_sem); > > *** DEADLOCK *** > > 2 locks held by touch/487: > #0: (sb_writers#10){.+.+.+}, at: mnt_want_write+0x41/0xb0 > #1: (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870 > > stack backtrace: > CPU: 0 PID: 487 Comm: touch Not tainted 4.12.0-rc7+ #9 > Call Trace: > dump_stack+0xdb/0x185 > print_circular_bug+0x45b/0x790 > __lock_acquire+0x1f74/0x38f0 > lock_acquire+0x1cc/0x600 > down_write+0x74/0x110 > cifsFileInfo_put+0x88f/0x16a0 > cifs_setattr+0x992/0x1680 > notify_change+0x61a/0xa80 > utimes_common+0x3d4/0x870 > do_utimes+0x1c1/0x220 > SyS_utimensat+0x84/0x1a0 > entry_SYSCALL_64_fastpath+0x1f/0xbe > > Fixes: 19dfc1f5f2ef03a52 ("cifs: fix the race in cifs_writev()") > Signed-off-by: Rabin Vincent <rabinv@axis.com> > --- > fs/cifs/file.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > index fcef706..d16fa55 100644 > --- a/fs/cifs/file.c > +++ b/fs/cifs/file.c > @@ -2810,12 +2810,12 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) > struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server; > ssize_t rc; > > + inode_lock(inode); > /* > * We need to hold the sem to be sure nobody modifies lock list > * with a brlock that prevents writing. > */ > down_read(&cinode->lock_sem); > - inode_lock(inode); > > rc = generic_write_checks(iocb, from); > if (rc <= 0) > @@ -2828,11 +2828,11 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) > else > rc = -EACCES; > out: > + up_read(&cinode->lock_sem); > inode_unlock(inode); > > if (rc > 0) > rc = generic_write_sync(iocb, rc); > - up_read(&cinode->lock_sem); > return rc; > } > > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-cifs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/cifs/file.c b/fs/cifs/file.c index fcef706..d16fa55 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -2810,12 +2810,12 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server; ssize_t rc; + inode_lock(inode); /* * We need to hold the sem to be sure nobody modifies lock list * with a brlock that prevents writing. */ down_read(&cinode->lock_sem); - inode_lock(inode); rc = generic_write_checks(iocb, from); if (rc <= 0) @@ -2828,11 +2828,11 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from) else rc = -EACCES; out: + up_read(&cinode->lock_sem); inode_unlock(inode); if (rc > 0) rc = generic_write_sync(iocb, rc); - up_read(&cinode->lock_sem); return rc; }