linux/fs/select.c, branch v5.11

poll: fix performance regression due to out-of-line __put_user()

2021-01-08T19:06:29Z

The kernel test robot reported a -5.8% performance regression on the "poll2" test of will-it-scale, and bisected it to commit d55564cfc222 ("x86: Make __put_user() generate an out-of-line call"). I didn't expect an out-of-line __put_user() to matter, because no normal core code should use that non-checking legacy version of user access any more. But I had overlooked the very odd poll() usage, which does a __put_user() to update the 'revents' values of the poll array. Now, Al Viro correctly points out that instead of updating just the 'revents' field, it would be much simpler to just copy the _whole_ pollfd entry, and then we could just use "copy_to_user()" on the whole array of entries, the same way we use "copy_from_user()" a few lines earlier to get the original values. But that is not what we've traditionally done, and I worry that threaded applications might be concurrently modifying the other fields of the pollfd array. So while Al's suggestion is simpler - and perhaps worth trying in the future - this instead keeps the "just update revents" model. To fix the performance regression, use the modern "unsafe_put_user()" instead of __put_user(), with the proper "user_write_access_begin()" guarding in place. This improves code generation enormously. Link: https://lore.kernel.org/lkml/20210107134723.GA28532@xsang-OptiPlex-9020/ Reported-by: kernel test robot Tested-by: Oliver Sang Cc: Al Viro Cc: David Laight Cc: Peter Zijlstra Signed-off-by: Linus Torvalds

fs: Replace zero-length array with flexible-array member

2020-10-29T22:22:59Z

There is a regular need in the kernel to provide a way to declare having a dynamically sized set of trailing elements in a structure. Kernel code should always use “flexible array members”[1] for these cases. The older style of one-element or zero-length arrays should no longer be used[2]. [1] https://en.wikipedia.org/wiki/Flexible_array_member [2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays Signed-off-by: Gustavo A. R. Silva

pselect6() and friends: take handling the combined 6th/7th args into helper

2020-05-29T23:10:42Z

... and use unsafe_get_user(), while we are at it. Signed-off-by: Al Viro

y2038: syscalls: change remaining timeval to __kernel_old_timeval

2019-11-15T13:38:29Z

All of the remaining syscalls that pass a timeval (gettimeofday, utime, futimesat) can trivially be changed to pass a __kernel_old_timeval instead, which has a compatible layout, but avoids ambiguity with the timeval type in user space. Acked-by: Christian Brauner Acked-by: Rafael J. Wysocki Signed-off-by: Arnd Bergmann

fs/select.c: use struct_size() in kmalloc()

2019-07-17T02:23:25Z

One of the more common cases of allocation size calculations is finding the size of a structure that has a zero-sized array at the end, along with memory for some number of elements for that array. For example: struct foo { int stuff; struct boo entry[]; }; size = sizeof(struct foo) + count * sizeof(struct boo); instance = kmalloc(size, GFP_KERNEL); Instead of leaving these open-coded and prone to type mistakes, we can now use the new struct_size() helper: instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL); Also, notice that variable size is unnecessary, hence it is removed. This code was detected with the help of Coccinelle. Link: http://lkml.kernel.org/r/20190604164226.GA13823@embeddedor Signed-off-by: Gustavo A. R. Silva Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

select: shift restore_saved_sigmask_unless() into poll_select_copy_remaining()

2019-07-17T02:23:24Z

Now that restore_saved_sigmask_unless() is always called with the same argument right before poll_select_copy_remaining() we can move it into poll_select_copy_remaining() and make it the only caller of restore() in fs/select.c. The patch also renames poll_select_copy_remaining(), poll_select_finish() looks better after this change. kern_select() doesn't use set_user_sigmask(), so in this case poll_select_finish() does restore_saved_sigmask_unless() "for no reason". But this won't hurt, and WARN_ON(!TIF_SIGPENDING) is still valid. Link: http://lkml.kernel.org/r/20190606140915.GC13440@redhat.com Signed-off-by: Oleg Nesterov Cc: Al Viro Cc: Arnd Bergmann Cc: David Laight Cc: Davidlohr Bueso Cc: Deepa Dinamani Cc: Eric W. Biederman Cc: Eric Wong Cc: Jason Baron Cc: Jens Axboe Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

select: change do_poll() to return -ERESTARTNOHAND rather than -EINTR

2019-07-17T02:23:24Z

do_poll() returns -EINTR if interrupted and after that all its callers have to translate it into -ERESTARTNOHAND. Change do_poll() to return -ERESTARTNOHAND and update (simplify) the callers. Note that this also unifies all users of restore_saved_sigmask_unless(), see the next patch. Linus: : The *right* return value will actually be then chosen by : poll_select_copy_remaining(), which will turn ERESTARTNOHAND to EINTR : when it can't update the timeout. : : Except for the cases that use restart_block and do that instead and : don't have the whole timeout restart issue as a result. Link: http://lkml.kernel.org/r/20190606140852.GB13440@redhat.com Signed-off-by: Oleg Nesterov Acked-by: Linus Torvalds Cc: Al Viro Cc: Arnd Bergmann Cc: David Laight Cc: Davidlohr Bueso Cc: Deepa Dinamani Cc: Eric W. Biederman Cc: Eric Wong Cc: Jason Baron Cc: Jens Axboe Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

signal: simplify set_user_sigmask/restore_user_sigmask

2019-07-17T02:23:24Z

task->saved_sigmask and ->restore_sigmask are only used in the ret-from- syscall paths. This means that set_user_sigmask() can save ->blocked in ->saved_sigmask and do set_restore_sigmask() to indicate that ->blocked was modified. This way the callers do not need 2 sigset_t's passed to set/restore and restore_user_sigmask() renamed to restore_saved_sigmask_unless() turns into the trivial helper which just calls restore_saved_sigmask(). Link: http://lkml.kernel.org/r/20190606113206.GA9464@redhat.com Signed-off-by: Oleg Nesterov Cc: Deepa Dinamani Cc: Arnd Bergmann Cc: Jens Axboe Cc: Davidlohr Bueso Cc: Eric Wong Cc: Jason Baron Cc: Thomas Gleixner Cc: Al Viro Cc: Eric W. Biederman Cc: David Laight Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

signal: remove the wrong signal_pending() check in restore_user_sigmask()

2019-06-29T08:43:45Z

This is the minimal fix for stable, I'll send cleanups later. Commit 854a6ed56839 ("signal: Add restore_user_sigmask()") introduced the visible change which breaks user-space: a signal temporary unblocked by set_user_sigmask() can be delivered even if the caller returns success or timeout. Change restore_user_sigmask() to accept the additional "interrupted" argument which should be used instead of signal_pending() check, and update the callers. Eric said: : For clarity. I don't think this is required by posix, or fundamentally to : remove the races in select. It is what linux has always done and we have : applications who care so I agree this fix is needed. : : Further in any case where the semantic change that this patch rolls back : (aka where allowing a signal to be delivered and the select like call to : complete) would be advantage we can do as well if not better by using : signalfd. : : Michael is there any chance we can get this guarantee of the linux : implementation of pselect and friends clearly documented. The guarantee : that if the system call completes successfully we are guaranteed that no : signal that is unblocked by using sigmask will be delivered? Link: http://lkml.kernel.org/r/20190604134117.GA29963@redhat.com Fixes: 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add restore_user_sigmask()") Signed-off-by: Oleg Nesterov Reported-by: Eric Wong Tested-by: Eric Wong Acked-by: "Eric W. Biederman" Acked-by: Arnd Bergmann Acked-by: Deepa Dinamani Cc: Michael Kerrisk Cc: Jens Axboe Cc: Davidlohr Bueso Cc: Jason Baron Cc: Thomas Gleixner Cc: Al Viro Cc: David Laight Cc: [5.0+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

y2038: syscalls: rename y2038 compat syscalls

2019-02-06T23:13:27Z

A lot of system calls that pass a time_t somewhere have an implementation using a COMPAT_SYSCALL_DEFINEx() on 64-bit architectures, and have been reworked so that this implementation can now be used on 32-bit architectures as well. The missing step is to redefine them using the regular SYSCALL_DEFINEx() to get them out of the compat namespace and make it possible to build them on 32-bit architectures. Any system call that ends in 'time' gets a '32' suffix on its name for that version, while the others get a '_time32' suffix, to distinguish them from the normal version, which takes a 64-bit time argument in the future. In this step, only 64-bit architectures are changed, doing this rename first lets us avoid touching the 32-bit architectures twice. Acked-by: Catalin Marinas Signed-off-by: Arnd Bergmann