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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/8/2024 10:28 PM, Klara Modin wrote: > Hi, > > On 2024-11-15 16:30, Josef Bacik wrote: >> FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending >> on the faulting method. >> >> This pre-content event is meant to be used by hierarchical storage >> managers that want to fill in the file content on first read access. >> >> Export a simple helper that file systems that have their own ->fault() >> will use, and have a more complicated helper to be do fancy things with >> in filemap_fault. >> > > This patch (0790303ec869d0fd658a548551972b51ced7390c in next-20241206) > interacts poorly with some programs which hang and are stuck at 100 % > sys cpu usage (examples of programs are logrotate and atop with root > privileges). > > I also retested the new version on Jan Kara's for_next branch and it > behaves the same way. From linux-next20241206 onward we started hitting issues where KVM guests running kernel > next20241206 on AMD platforms fails to shutdown, hangs forever with below errors: [ OK ] Reached target Late Shutdown Services. [ OK ] Finished System Power Off. [ OK ] Reached target System Power Off. [ 128.946271] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Connection refused [ 198.945362] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 298.945402] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 378.945345] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 488.945402] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 558.945904] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 632.945409] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 738.945403] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected [ 848.945342] systemd-journald[93]: Failed to send WATCHDOG=1 notification message: Transport endpoint is not connected .. .. Bisecting the issue pointed to this patch. commit 0790303ec869d0fd658a548551972b51ced7390c Author: Josef Bacik Date: Fri Nov 15 10:30:29 2024 -0500 fsnotify: generate pre-content permission event on page fault Same issue exists with todays linux-next build as well. Adding below configs in the guest_config fixes the shutdown hang issue: CONFIG_FANOTIFY=y CONFIG_FANOTIFY_ACCESS_PERMISSIONS=y Regards, Srikanth Aithal > >> Signed-off-by: Josef Bacik >> --- >>  include/linux/mm.h |  1 + >>  mm/filemap.c       | 78 ++++++++++++++++++++++++++++++++++++++++++++++ >>  2 files changed, 79 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 01c5e7a4489f..90155ef8599a 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -3406,6 +3406,7 @@ extern vm_fault_t filemap_fault(struct vm_fault >> *vmf); >>  extern vm_fault_t filemap_map_pages(struct vm_fault *vmf, >>          pgoff_t start_pgoff, pgoff_t end_pgoff); >>  extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); >> +extern vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf); >> >>  extern unsigned long stack_guard_gap; >>  /* Generic expand stack which grows the stack according to >> GROWS{UP,DOWN} */ >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 68ea596f6905..0bf7d645dec5 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -47,6 +47,7 @@ >>  #include >>  #include >>  #include >> +#include >>  #include >>  #include >>  #include "internal.h" >> @@ -3289,6 +3290,52 @@ static vm_fault_t >> filemap_fault_recheck_pte_none(struct vm_fault *vmf) >>      return ret; >>  } >> >> +/** >> + * filemap_fsnotify_fault - maybe emit a pre-content event. >> + * @vmf:    struct vm_fault containing details of the fault. >> + * @folio:    the folio we're faulting in. >> + * >> + * If we have a pre-content watch on this file we will emit an event >> for this >> + * range.  If we return anything the fault caller should return >> immediately, we >> + * will return VM_FAULT_RETRY if we had to emit an event, which will >> trigger the >> + * fault again and then the fault handler will run the second time >> through. >> + * >> + * This is meant to be called with the folio that we will be filling >> in to make >> + * sure the event is emitted for the correct range. >> + * >> + * Return: a bitwise-OR of %VM_FAULT_ codes, 0 if nothing happened. >> + */ >> +vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf) > > The parameters mentioned above do not seem to match with the function. > >> +{ >> +    struct file *fpin = NULL; >> +    int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_ACCESS; >> +    loff_t pos = vmf->pgoff >> PAGE_SHIFT; >> +    size_t count = PAGE_SIZE; >> +    vm_fault_t ret; >> + >> +    /* >> +     * We already did this and now we're retrying with everything >> locked, >> +     * don't emit the event and continue. >> +     */ >> +    if (vmf->flags & FAULT_FLAG_TRIED) >> +        return 0; >> + >> +    /* No watches, we're done. */ >> +    if (!fsnotify_file_has_pre_content_watches(vmf->vma->vm_file)) >> +        return 0; >> + >> +    fpin = maybe_unlock_mmap_for_io(vmf, fpin); >> +    if (!fpin) >> +        return VM_FAULT_SIGBUS; >> + >> +    ret = fsnotify_file_area_perm(fpin, mask, &pos, count); >> +    fput(fpin); >> +    if (ret) >> +        return VM_FAULT_SIGBUS; >> +    return VM_FAULT_RETRY; >> +} >> +EXPORT_SYMBOL_GPL(filemap_fsnotify_fault); >> + >>  /** >>   * filemap_fault - read in file data for page fault handling >>   * @vmf:    struct vm_fault containing details of the fault > > > >> @@ -3392,6 +3439,37 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) >>       * or because readahead was otherwise unable to retrieve it. >>       */ >>      if (unlikely(!folio_test_uptodate(folio))) { >> +        /* >> +         * If this is a precontent file we have can now emit an event to >> +         * try and populate the folio. >> +         */ >> +        if (!(vmf->flags & FAULT_FLAG_TRIED) && >> +            fsnotify_file_has_pre_content_watches(file)) { >> +            loff_t pos = folio_pos(folio); >> +            size_t count = folio_size(folio); >> + >> +            /* We're NOWAIT, we have to retry. */ >> +            if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) { >> +                folio_unlock(folio); >> +                goto out_retry; >> +            } >> + >> +            if (mapping_locked) >> +                filemap_invalidate_unlock_shared(mapping); >> +            mapping_locked = false; >> + >> +            folio_unlock(folio); >> +            fpin = maybe_unlock_mmap_for_io(vmf, fpin); > > When I look at it with GDB it seems to get here, but then always jumps > to out_retry, which keeps happening when it reenters, and never seems to > progress beyond from what I could tell. > > For logrotate, strace stops at "mmap(NULL, 909, PROT_READ, MAP_PRIVATE| > MAP_POPULATE, 3, 0". > For atop, strace stops at "mlockall(MCL_CURRENT|MCL_FUTURE". > > If I remove this entire patch snippet everything seems to be normal. > >> +            if (!fpin) >> +                goto out_retry; >> + >> +            error = fsnotify_file_area_perm(fpin, MAY_ACCESS, &pos, >> +                            count); >> +            if (error) >> +                ret = VM_FAULT_SIGBUS; >> +            goto out_retry; >> +        } >> + >>          /* >>           * If the invalidate lock is not held, the folio was in cache >>           * and uptodate and now it is not. Strange but possible since we > > Please let me know if there's anything else you need. > > Regards, > Klara Modin