Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.
Linus Torvalds
authored
Pull mount_setattr fix from Christian Brauner: "The recent cleanup in e257039f ("mount_setattr(): clean the control flow and calling conventions") switched the mount attribute codepaths from do-while to for loops as they are more idiomatic when walking mounts. However, we did originally choose do-while constructs because if we request a mount or mount tree to be made read-only we need to hold writers in the following way: The mount attribute code will grab lock_mount_hash() and then call mnt_hold_writers() which will _unconditionally_ set MNT_WRITE_HOLD on the mount. Any callers that need write access have to call mnt_want_write(). They will immediately see that MNT_WRITE_HOLD is set on the mount and the caller will then either spin (on non-preempt-rt) or wait on lock_mount_hash() (on preempt-rt). The fact that MNT_WRITE_HOLD is set unconditionally means that once mnt_hold_writers() returns we need to _always_ pair it with mnt_unhold_writers() in both the failure and success paths. The do-while constructs did take care of this. But Al's change to a for loop in the failure path stops on the first mount we failed to change mount attributes _without_ going into the loop to call mnt_unhold_writers(). This in turn means that once we failed to make a mount read-only via mount_setattr() - i.e. there are already writers on that mount - we will block any writers indefinitely. Fix this by ensuring that the for loop always unsets MNT_WRITE_HOLD including the first mount we failed to change to read-only. Also sprinkle a few comments into the cleanup code to remind people about what is happening including myself. After all, I didn't catch it during review. This is only relevant on mainline and was reported by syzbot. Details about the syzbot reports are all in the commit message" * tag 'fs.fixes.v5.18-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: fs: unset MNT_WRITE_HOLD on failure
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