On Sun 2022-10-16 14:30:30, Petr Pavlu wrote: > During a system boot, it can happen that the kernel receives a burst of > requests to insert the same module but loading it eventually fails > during its init call. For instance, udev can make a request to insert > a frequency module for each individual CPU when another frequency module > is already loaded which causes the init function of the new module to > return an error. > > The module loader currently serializes all such requests, with the > barrier in add_unformed_module(). This creates a lot of unnecessary work > and delays the boot. It can prevent udev from loading drivers for other > devices and might cause timeouts of services waiting on them and > subsequently a failed boot. > > The mentioned serialization was introduced as a side-effect of commit > 6e6de3dee51a. The kernel before that merged some of same load requests > although it was more by accident and relied on specific timing. The > patch brings this behavior back in a more explicit form. > > The logic is improved as follows: > * A check whether a module load matches an already loaded module is > moved right after a module name is determined. -EEXIST continues to be > returned if the module exists and is live, -EBUSY is returned if > a same-name module is going. > * A new reference-counted shared_load_info structure is introduced to > keep track of duplicate load requests. Two loads are considered > equivalent if their module name matches. In case a load duplicates > another running insert, the code waits for its completion and then > returns -EEXIST or -EBUSY depending on whether it succeeded. > > Moving the check for same-name module loads earlier has also a positive > effect on reducing memory pressure. For instance, David Hildenbrand and > Lin Liu reported [1] that when KASAN_INLINE is enabled (resulting in > large module size), with plenty of devices that udev wants to probe and > with plenty of CPUs that can carry out that probing concurrently, the > system can actually run out of module vmap space and trigger vmap > allocation errors. This is fixed by the patch too as it avoids duplicate > layout_and_allocate() work. > > [1] https://lore.kernel.org/all/20221013180518.217405-1-david@xxxxxxxxxx/ > > Fixes: 6e6de3dee51a ("kernel/module.c: Only return -EEXIST for modules that have finished loading") > Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> > Signed-off-by: Petr Pavlu <petr.pavlu@xxxxxxxx> All these tags should be in the order of (logical) appearance. Somethings like: Suggested-by: if any Signed-off-by: author of the patch Acked-by: in order of appearance Revived-by: in order of appearance Tested-by: in order of appearance Signed-off-by: committer (upstream maintainer) I know that I provided Reviewed-by before you did the final changes. Well, you could use my tag only when you did only cosmetic changes or changes that I requested. You expect that I would agree with the patch even after it was updated. Best Regards, Petr
